Canon BJC-250 printer problems

Hi, I acquired a 2nd-hand Canon BJC-250 printer back in January. It seemed to work fine, as the test page printed* and Windows 2K SP4 auto-detected the printer when it was switched on (which is good because I got a "data error (cyclic redundancy check)" when trying to copy the drivers from floppy disk to my laptop). On closer inspection though, all doesn't appear to be fine. I thought I had a black only cartridge installed (which came with the printer), but it turns out to be a colour one. Now the problem occurs when I print a page with black text. The text is printed with alternating black and green lines, instead of just black. Now I never saw this problem at work when we used the same printer model, but that may have been a black only cartridge. Is this problem a side effect of having a colour cartridge, bubble jet printers, or indicative of a problem with the read head / cartridge? I have very little experience with printers and would appreciate any pointers anyone can offer. I hope it fits withing the 10 year rule... not sure how old the printer model is. *The test page requires no input from the computer, so I ruled out a possible driver issue. Regards, Andrew B aliensrcooluk at yahoo.co.uk