The alarm light is on and it says to check paper size

The in use alarm appears to be related to fax reception and printing. There are some options below that you could try:-
Memory Reception If the machine receives a fax under one of the following conditions, it will not be able to print the received fax and will store it in its memory. The In Use/Memory lamp is lit and Received in memory is displayed on the LCD. When the problem is resolved as described, the fax stored in memory is printed automatically.

• Ink has run out: Replace the FINE Cartridge.
  Routine Maintenance
  Note
  
  • You can set the machine to forcibly print a received fax even if the ink has run out.
    However, part or all of the fax may not be printed since the ink has run out.
    Also, the contents of the fax will not be stored in memory.
    If the ink has already run out, we recommend that OFF be selected for Auto print in FAX user settings to store the received fax in memory and print the fax manually after replacing the FINE Cartridge. After you replace the FINE Cartridge and select ON for Auto print, the fax stored in memory will be printed automatically.
• Paper has run out: Load the paper and press the OK button.
• A different size of paper from that specified by Page size is loaded:
  Load the same size of paper as that specified by Page size, then press the OK button.
• Page size is set to other than A4, 8.5"x11"(LTR), or Legal (or 8.5"x14"):
  Set Page size to A4, 8.5"x11"(LTR), or Legal (or 8.5"x14").
• Media type is set to other than Plain paper:
  Set Media type to Plain paper.
• You pressed the Stop button to cancel printing of a fax:
  Press the FAX button
  

Alternatively turn the printer off, open the devices and printers section of Control Panel, right click on your printer and select "see what's printing" and left click on this. A window will pop up which may or may not contain a list of documents. If it does these must be cancelled (Menu - Printer - Cancel all documents). Once all documents have gone from the list turn the printer on and try to print.
Other than the above suggestions I would need to know more about your OS and exact problem. Hope this helps.

Did you trying hitting an Ok button, green button, etc to confirm legal size paper, maybe it wants you to confirm paper size. Also legal is 8.5x14, did you select legal or enter the size as a custom page?

If the machine receives a fax under one of the following conditions, the machine will not be able to print the received fax and will automatically store it in its memory.Ink has run out while receiving a fax.Paper has run out while receiving a fax.

• Paper other than A4, Letter, or Legal-sized papers are loaded.
  
• OFF is selected for Auto Print in User Settings.
  
• You pressed the Stop button to cancel printing of a fax.

1. Make sure that the plain paper is loaded in the Rear Tray.

2. Display the Memory reference screen.
(1) Press the FAX button, and press the Menu button.
(2) Use the (-) or (+) button to select Memory reference, and press the OK button.

3. Print all the received documents in the memory.
(1) Use the (-) or (+) button to select Print all RX docs.

• To print the list of documents in the memory, select Print memory list.
  
• To print a specified document, select Print specified doc..
  
• To delete a specified document, select Delete specified doc..
  
• To delete all documents in the memory at the same time, select Delete all documents.
  

(2) Press the OK button.
(3) Use the (-) or (+) button to select Yes, and press the OK button.

The machine starts printing documents in the memory one by one.

(4) Use the (-) or (+) button to select Yes



To keep the document in the memory, select No.

(5) Press the OK button.

• The deletion confirmation screen will appear each time after one document is printed. Repeat the same procedure until all documents are printed.

try by pressing function and then data registration and set/ok!It will say user settings and use the arrows up/down to scroll to printer settings,press set/ok and scroll to paper size,press set/ok and if its on a4 use the arrows to get to LTR and press set/ok!If that works then u will need to have the registration sensor at the back looked at as it is most likely not falling into position after the paper has passed it!Good Luck and remember to vote PSE!!

go print -> properties -> page setup -> print options -> tick Disable the paper source setting of the application software -> hit ok and go back to "main" -> select the paper source that you want and hit ok ok and print

You must be set you machine from program key
1> press menu>paper size>A4/Letter/set OK
after print or copy your requirement size.

If your Canon MX-310 has been set up to print faxes as they are received, then what is actually in memory is a "received fax report". If you select a particular fax in this report, it will print the first page of the fax to remind you of the content.

Your Canon MX-310 will store fax documents in memory if:

• Ink is low or has run out
• The paper size and type is not set correctly
• Paper has run out
• The Output Tray is closed

if you still have the paper manual it's on page 54 and 55
basically you have to press fax button, then press the menu button, then use the right or left arrows (on the side of the ok button) to select "memory reference" then press "ok", then press the arrows again to print which document in memory you want to print (usually the most recent is listed) then press "ok" again.

finally press the arrows to select "yes" to print only the first page or "no" to print the entire document and press the ok button one last time. it should print.

if you are still receiving a "change paper size" type error, go ahead and press the fax button, then the settings button, use the arrows to select your paper size, press ok, then select media type, in this case "plain paper" and press "ok"

that should do it.

It seemed to work, It began after I downloaded a document from the Russian government and translated it in Google.

Solution #3 solved it for me. The report kept printing over and over, so I used the menus (roughly) mentioned in Soluton #3 by guest.

My problem was the printer was trying to print the TX Error Report with the image attached. That made the report too big for standard sized paper, so the machine kept telling me to check the paper size, and I'd hit 'OK', and that made the machine try to print the report again, for it continued to think it had not printed a complete report.

Here's what I did...

Go to: Fax Menu
Arrow right ( >) to Maintenance/Settings, hit, 'OK'
Arrow right to (>) to Device Settings, hit 'OK',
Fax Settings, hit 'OK',
Arrow down ( v ) to TX Settings, hit 'OK',
Arrow down ( v ) to TX Report, OK
Select 'Print error only', hit 'OK',
Attach TX image, Select 'NO', hit 'OK"

With the instruction to not attach the TX image, it will print out the error report without the TX image, the report will fit on the paper, and it will clear this problem.

Good luck!