Envelopes won't print in black

I have a new Lexmark X5150 All in One (same as Dell A940).  I am using a Dell Dimension 2400, running Windows XP, using Word Perfect.  When printing envelopes, every third letter is green.  The correct font color (whether it's black, blue, red, etc. only appears for a couple of letters in between).  I have tried changing print preferences to "black only", and I have re installed the print driver, but nothing helps. Sometimes the envelope is just sent through blank.  Since color or black prints correctly on all documents except envelopes, I don't think the problem is with the cartridges.  Any suggestions would be appreciated!