I'm having the same problem--just started today. Have had both Acrobat Standard 7 and Reader 8 installed for quite some time without problems--now all of a sudden I can't get my kids' school worksheets and answer keys!!! (They attend school online--this is a major issue!!!)
Thought it was a Firefox problem since it started when opening PDFs in Firefox 3, but I have the same problem in IE 7 *AND* when opening PDFs directly in either Acrobat *OR* Reader: The file opens for a couple of seconds, but then: "Adobe Acrobat 7.0 has encountered a problem and needs to close," or a similar message about Reader. If I'm quick enough, I can just barely save the file before it crashes--but then when I try to manually open it, same crash message.
SOMEBODY HELP!!! This problem is catastrophic for work and school in this house!!! (And I can't imagine if the same thing began to happen on our office computers!)
Uninstall Reader. Re-install Acrobat.