Problem with a MATRIX printer...

I have a small application I've programmed to print bills on a matrix
printer.
It just print a few lines on a paper.

My code is quite standard.

BeginDoc
Print the lines
EndDoc...

But my problem is that the printer keeps printing %5% on the top left corner
of the paper before printing the rest.

Anybody knows where that kind stuff migh come from and how to prevent it.

Thanks to any replies.