Unusual paper size

it seems that on your model you can only use legal size paper on tray 1 & 2, then you have to set the paper size.
here is a link to instructions for your model.
http://download.brother.com/welcome/doc002258/mfc9840_uk_usr_b.pdf

The printer should accpet every paper only requires adjusting the feeder area fo every new brand paper that is inserted on device. Inspect the devices feeder compartment for appropiate size requested of the paper. Also, the printing paper has size adjustment details required to fit into the printer. Once observed, the feeder compartment would require manually adjusting to fit new paper size to achieve printerbility. Also, power on the computer to test print the new adjustments. The printer commnads too allows to sleect the appropiate shapes requested considerign the type of pape inserted in feeder comparments. Circumspectively, perform printer feeder compartment adjustments and test print a page to ascertain the most possible condition ot the new settings.

Problem 1 :
As far as the machine printing 2 pages per job. To fix this it's usually the default number of copies the printer is set to. To change/ confirm the setting is set to one:
Press the menu button
Arrow down to -> Printing, Press the green check to enter the menu
Arrow down to -> Copies Press the green check to enter the menu
Change or confirm the value = 1, (Based on your question this might be set to 2) Press the green save the value.
* If your number of copies is set to 1 and the machine is still printing 2 copies, then the problem relays in your print driver.

Problem 2: General Misprint Error message something like 41.3
2 things to check:

1st - Press the menu button
Arrow down to Paper Handling, Press the green check to enter the menu
Now you will see options like Tray 1 size - Tray 1 type. Here their will be a option for each tray installed on your machine. You will go into each tray option and confirm the paper size and type.
Example
Tray 1 Size = Envelope #10 (This is the manual feed tray)
Tray 1 Type = Envelope
Tray 2 Size = Letter
Tray 2 Type = Plain

To perform arrow down to tray X size press the green check to access the menu, arrow up or down to select your paper size. Once the paper size is selected press the green check to save it. repeat for each tray.

2nd -
Pull out your tray and remove the paper, towards back of the tray you will see a guide (Tab) in the middle of the tray which allows you to expand the tray to accept various paper sizes, Please confirm the guide is set to the correct type. If your using letter, make sure the guide is set to letter (LTR) you can see these codes by looking at the base of the guide, their is a little arrow pointer.

Hope this helps

Loading Paper
1 Adjust the guides to the position for the paper size you are using.
2 Fan the paper well.
Push down the paper lever. Load the paper (with the lever down). Make sure the print side is toward the fax machine and the paper level is stacked below the paper mark. The feeder can hold up to 200 sheets of paper, or up to 10
envelopes.
Acceptable Paper
The FAX/MFC can handle paper that has the following specifications.
But please note that you can receive fax messages only on Letter, Legal and A4 paper. If you use legal or A4, change the Paper Size setting: (Menu/Set, 1, 1.)
Paper Type Paper Size
Cut sheet Letter, A4, Legal, B5, A5, Executive,
Custom size 2.75-8.5 × 5-14 inches (70-216 × 127-356 mm)
Envelopes DL, C5, COM-10, Monarch
Post Card 2.75-8.5 × 5-11 inches (70-216 × 127-279 mm)
Organizer Day-Timer® J, K, L, M 2.75-8.5 × 5-11 inches (70-216 × 127-279 mm)
Labels and Transparencies 2.75-8.5 × 5-14 inches (70-216 × 127-356 mm)

You are most likely getting this message because of a paper size mis-match. For example, you are sending a print job as letter size but your printer is set to or has a4 size installed. When the printer sees that the print job is not a matched size to the paper in the tray, it will look to the manual feed tray for paper to print on, hopefully the correct size. Make sure your paper setting in printer properties on your computer match the paper in the printer and the print job "page setup" is also the same size/

Need to set A4 size default on the printer driver itself.
Go to Printers and Faxes / Konica Minolta 2490MF right click/ Printing preferences /
Create a "Easy Set" with a new name. Set all paper sizes to A4. Save the new settings to the new Easy Set.
Click apply.

should be o.k.

You just stated the problem yourself!!!!!!!!!!!!!!!!!!!!!

Are you using Letter or Legal?? then the tray need to be set to that particular size.

If using Legal set to Legal, otherwise the machine will automatically know you are using the wrong size.

"Check paper size" means that the paper in the machine doesn't match the size selected in the setup.

To change the paper size:
1. Press the Function button.
2. Press the Data Registration button.
3. Press Set button.
4. Use up or down arrows until you see PRINTER SETTINGS.
5. Press Set button.
6. Use up or down arrows until you see PAPER SIZE.
7. Press Set button.
8. Use up or down arrows until you see type of paper in the paper tray (LTR, LGL, A4).
9. Press Set button.
10. Press Stop/Reset button.

Machine should now print out the fax that was received in memory.

From a Windows Operating System:

1. From the computer, open the document to be printed within an application program.
2. Click on [File] on the toolbar, and then click [Print]. The Print window will be displayed.
3. Click on the [Properties] button, or the [Printing Preferences] button. The Properties or Printing Preferences window will be displayed.
4. Click on the [Paper / Quality] tab.
   
   NOTE: Most applications will automatically provide the page size information to the driver. If not, steps 8 - 10 describe how to create a custom page size.
   
   
5. Select the required paper size from the Document Size pull down menu, if available.
6. If the required custom paper size is not available click on the [My Customer Sizes…] button.
7. To create a new custom paper size setting click on the [New] button.
8. In the Name field enter the name to be given to the custom paper size. For example 127 mm x 394 mm (5 in. x 10 in.)
9. In the Width field enter the width of the custom paper size.
   
   NOTE: The width should always be the short edge of the paper. For example, if the custom size is 127 mm by 394 mm (5 inches by 10 inches), the width must be set to 127 mm (5 inches) regardless of the orientation of the document or the feed method on the printer.
   
   
10. In the Height field enter the height of the custom paper size.
    
    NOTE: The height should always be the long edge of the paper. For example, if the custom size is 127 mm by 394 mm (5 inches by 10 inches), the height must be set to 394 mm (10 inches) regardless of the orientation of the document or the feed method on the printer.
    
    
11. Click on [Save]
12. Click on [Close].
13. Select the required paper size from the Document Size pull down menu.
14. Click on [OK] twice to print

From a Mac OSx:

1. Click on [File] on the application toolbar, and then click on [Page Setup]. The Page Setup window will be displayed.
2. From the Printer Description pull-down menu, select the correct PPD file for your printer.
3. Select the custom paper size for your document from the Paper Size pull-down menu.
4. If the required custom paper size is not available click on the [Manage Custom Sizes…]. The Custom Page Sizes window will be displayed
5. To create a new custom paper size setting click on the [+] button.
6. Double click on [Untitled] and enter the name to be given to the custom paper size.
7. At the Page Size field enter the width and height of the custom paper size.
8. Click on [OK] twice.

This machine will only print certain sizes as borderless. A5 is not one of them. You can use the following media with this feature: Matte Paper - Heavyweight: A4, Letter Premium Glossy Photo Paper:A4, Letter, 5 x 7", 10 x 15 cm/4 x 6", 8 x 10" Photo Paper:A4 Premium Semigloss Photo Paper:A4, Letter, 10 x 15 cm/4 x 6" Glossy Photo Paper:Letter, 10 x 15 cm/4 x 6" As you can see A5 is not in the list, therefor you will not be able to print A5 borderless via the normal means.