Are you printing from a script or the File menu?
Did you make any changes in FileMaker version, operating system (version or update), or printer used?
I do print from a small script but the problem occurs regardless if I use the scrip or print from the File menu or print from page preview.
One thing I did do recently is in my entry window, I increased my input window larger than my page size horizontally. Since the script takes me to a different layout I didn't think that would be a problem.
Running FMP 8.5 on Mac OS 10.4.11 when I encountered this issue.
Opened the same file on a different computer running FMP 11.0v3 on Mac OS 10.5.8 the first output page printed correctly the second output only printed half the page.
It may be that your file and or some of its layouts are corrupted. (My earlier questions were intended to rule out other possible causes.)
Test a recovered copy of the file and see if you get any differences. (Even if recover reports no problems found.)
Try rebuilding on of these layouts from scratch in your file (dont' copy paste any elements from a layout that doesn't print correctly) and see if it prints correctly.