Digital BW, The Print

I am printing with a 4000 on a Mac using QuadtoneRIP 2.1., Premium Luster 
roll paper.  It has been acting strange lately. It will start to print just fine, 
somewhere in the middle it will stop, backup and start to print over the top of 
where it already printed. One of the strange things is that it will print a couple 
prints normally and then start acting up. I just printed one print twice; the first 
one was find the second was not.

Please help, this is driving me crazy.

Thanks