We saw the same symptoms as you describe.
It turned out that the new sandbox feature in Reader X is not compatible with Re-Directed "Application Data" folders.
Disabling the sandbox safety feature (via a special registry setting) appears to be a workaround, but somehow we now feel less safe.
Folder redirection involves group policy as used in large corporations with IT teams to manage large numbers of PCs in companies.
For example, in corporate environments, users My Documents and AppData folders are often re-directed at a secure server share, so that people's documents/photos/mp3s they save into my documents are secured on a server, instead of scattered about on various PCs. Home users never use this technology.
However, If you've got Adobe Reader X installed to a different DRIVE to the one where your APPDATA folder is, then you might get the same effect.
I guess this could also happen to peole with Windows installed on their D: drives, and Adobe installed on the C: drive, or similar.
Thanks.. how did you disable the sandbox safety feature vai a special
you should probably read this: http://kb2.adobe.com/cps/860/cpsid_86063.html
and maybe this: http://learn.adobe.com/wiki/display/security/Protected+Mode+FAQ
It is however possible that this problem doesn't apply to your specific circumstances so this workaround may not necessarily help you.
Normally you would use the GUI to disable protected mode, but if your Reader crashes on launch, then you will have trouble accessing that option in the preferences to make the change. If all of this applies to you, the reg key is:
Well fixed the problem. After reading your attachments I came to the
conclusion this is more hassle than it is worth as it seems Reader X is
compromised . Solution: ignore the problem by downloading an earlier
version 8. Wonderful, now I can open pdf files.