QTR-Quadtone RIP

Hi - I am using an R-1800, sometimes it loads just fine and other 
times it will not take the paper in, while other times it takes the 
paper and just passes it through.  Is this a common problem or do I 
have a defective printer.  I have tried thicker 250gsm and regular 
20lb copy paper and it does bad things with both. 
Any thoughts.....Michael G