Do a Google search for prop res DLL not loaded and you'll see a lot of support threads from the last 5 or 6 years for various different software that have had that problem, it sounds like a fault with Lexmark drivers or with their installation routine. In the case mentioned in this support thread, it looks like copying a Lexmark DLL file into the \system 32\ folder solved it for some posters in that thread.
http://www.proz.com/forum/office_applications/30138-error_message_prop_res_dll_not_loaded_in_word_how_can_i_fix_this.html

My advice is to download the latest version of drivers for that printer, uninstall your current drivers and make sure you delete the program files folder they were installed in, and then install the downl0aded driver pack.

Sorry, I don't know why that problem just happened with Firefox 4 and didn't happen with an earlier version of Firefox. If you want to revert to the older version of Firefox see this.
http://support.mozilla.com/en-US/kb/Installing+a+previous+version+of+Firefox

http://www.mozilla.com/en-US/firefox/all-older.html

Download new drivers didn't help, but your link led me to the following which solved the problem. Thanks (to you and gpartridge)!

gpartridge English RESOLUTION Apr 6, 2006

goto c:\windows\system32\spool\drivers\w32x86\Lexmark_x1100_seriesf27b and copy lxbkprpr.dll to c:\windows\system32

if you don't have c:\windows\system32\spool\drivers\w32x86\Lexmark_x1100_seriesf27b then just search for the dll.

This will resolve the issue.

Don't buy lexmark printers cos lexmark don't know what day it is.

I had the same problem with a Lexmark 1270 and solved the problem following the advice of char49, as follows:

goto c:\windows\system32\spool\drivers\w32x86\Lexmark_x1100_seriesf27b and copy lxbkprpr.dll to c:\windows\system32

The only difference to the above, with my printer, being that I selected: /Lexmark_1200_series8142 and copied the file: lxczprpr.dll

As there are so many printers in the Lexmark family, I would suggest that the first four or more characters represent the make and model and therefore one should find and copy the file containing: prpr.dll

Many thanks to char49 and other contributors who led to this solution.

I had the same problem with the Lexmark X1270 all-in-one printer. Microsoft has a page for fixing the problem with the Lexmark 1100 series printer but is not applicable to the X1270 as the dlls are not there.

Following the help from from Geebee25 above I did what he suggested. In detail: Go to c:\windows\system32\spool\drivers\w32x86\ Lexmark_1200_series8142 and copy lxczprpr.dll to c:\windows\system32

Works a treat! Note the problem only only existed when printing from Firefox so maybe MS have already included a fix for printing from MS Office suite of programs.