Will not select legal paper when printing and faxing, letter only.

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.

The receiving fax must have legal size paper available and their machine set to auto reduction.

This document explains the different results obtained when using or not using the Automatic Reduction (or Auto Reduction) Feature. The following issues usually result when the Automatic Reduction feature is not set correctly:

• Faxes printing too small
• Faxes printing on more than one page
• A blank page ejecting between each printed fax page

This feature can be turned ON (the default) or OFF from the Advanced Fax Features menu. The two main purposes of the Auto Reduction feature

• Fits a received fax page onto the paper size loaded in the paper tray and selected in the paper size setting of the Basic Fax Setup. For example; if letter size paper is loaded in the paper tray and selected in the fax settings and a legal size document is received, each page will be reduced and printed on one letter sized paper.
• Allows the addition of the fax header margin at the top of every printed fax without extending the fax onto another page. The fax header is printed at the top of every fax received with identifying information about the fax sender. Since this increases the overall page length, the page must be reduced to fit onto one page. Auto reduction slightly shrinks the fax as it is received so the entire page will print on one piece of paper even though a top margin is allowed for the fax header.

no thats why it is not working the right way you have to use the semi gloss paper thats what it requiers

The problem is that you have a fax saved in memory that is the wrong size for the paper you have in the drawer. Probably it is a legal size, whereas you have letter size in the drawer.Just place some legal size paper in the by-pass tray to print.

I have a 9920 manual,could be the same.Try the following but if you get different displays don't change anything.Press function,should read FUNCTION SELECT , ENTER FUNCTION # .Enter 8, scroll to AUTO REDUCTION.(use COM STAT or HELP keys to scroll)Change to NO.Press stop to return to normal mode.If this procedure is not exactly the same for your model,then just search through the function settings and find AUTO REDUCTION and set to no.

To answer more effectively - how is the printer connected to the iMac? Is it a USB connection, a printer cable, is the MFC 6800 connected to a print server, an AirPor, etc? A second question I have is if you are trying any kind of tricky printing such as manualduplex printing.

Also, a shot in the dark...Is the Auto Reduction set to on or off? To check:
1. Press MENU/SET, 2 (Fax), 1 (Setup Receive), then 4 (Auto Reduction).

2. Press the up or down navigation key (keys located above and below the
MENU/SET key) until the display shows "Reduction: ON?".

3. Press MENU/SET.

4. Press STOP/EXIT.

Another item to keep in mind:
You can use three sizes of paper for printing your faxes and
copies---letter, legal and A4. When you change the size of paper you ha
ve loaded in the Brother machine, you need to change the setting for the paper size so your Brother machine can fit the incoming
fax on the page. To set the Paper Size:

1. Press MENU/SET, 1 (General Setup), then 1 (Paper Size).

2. Press the up or down navigation key to select LETTER, LEGAL, or A4.

3. Press MENU/SET.

4. Press STOP/EXIT.

Change the cofiguration of the size in your fax machine see if accepts them then