I had a similar problem this week where pdf's would  no longer render after the latest Microsoft security update was installed. People @ work who had not applied the patch did not have the problem, but a co-workwer of mine who did apply it had the same problem (although it worked fine for us in firefox).
The newsest fix may have been trying to address this issue acrobat found recently:

http://www.networkcomputing.com/channels/security/showArticle.jhtml?articleID=196601020

suffice it to say installing Acrobat reader 8 fixed my issue (and my coworkers too)