It's a corrupt PDF. A PDF file has a pretty complex structure (described in the 750 page PDF reference document). Some PDF generators or PDF processors are not very good at following this specification, and you end up with corrupt PDF files. The symptoms of a corrupt PDF can range from things that Acrobat or Adobe Reader can correct to files that don't open at all. In your case, you have a PDF file that seems to open, but when you do certain things, you run into a problem.
One thing you can try is to save the PDF file under a new name (File>Save As in Acrobat). If you are very lucky, this will fix the problem, but in most cases, you will end up with an error message during the save as operation as well.
Complain to the creator of the PDF file - they've given you a bad file.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com