|I don't have a solution as much as a suggestion.|
Assuming you're not running 9.0, upgrade to the latest version. Maybe this'll solve your problem.
I suggest this mainly because of an issue I had with a online college form my daughter tried to access yesterday. Her system spat out an "corrupted file" error when we tried to open the PDF form. My system took forever to open it, after telling me that it was "created in a version that might not open correctly on your machine." 2 different machines, 2 different errors.
As soon as I upgraded both systems to 9.0, we were able to open the form.
I can only assume that more and more PDF's will be created in versions that are not backward compatible, so upgrading may be the only way to access them.