That's really strange... Maybe there are too many data for the Printing system that I use.
Try selecting only 200 movies at a time, print, then select next 200, etc.
(select first movie, then hold ctrl+shift+click on the 200th movie, it should select the 200 first, etc.)
I only select one movie at a time to print the cover.
Actual I have 259 movies listed but I always mark up one movie to print.
And since I reached the number 250 I cannot print a pic above 249....
That's really strange, since there are people with much more movies that do not have problems to print...
So any movie with a number above to 250 won't print ? Do you remember if you changed something when you added the 250th movie ? Are all pictures stored in catalog or linked to external files ?