The sandbox functionality in Adobe Reader X is known to conflict with some antivirus products.
I’ve installed Reader X at home with no issues. A post in the Symantec Connect forums indicates Adobe Reader X cannot open on computers that use the Network Threat Protection component of Symantec Endpoint Protection. The workaround for the moment is to disable Reader’s protected mode. I don’t use Network Threat Protection at home which is why I didn’t see any issues there.