I recently began experiencing a problem using Adobe Reader to open pdf documents that arrive as attachments to emails. I use Mozilla Thunderbird, ver. 7.0.1. When I click on a pdf attachment for the first time after booting the computer and starting Thunderbird, the pdf opens without a problem. If I try to open a second pdf, I get the message, "There was an error opening this document. This file cannot be found." The only way to open another pdf is to reboot my computer. Restarting Thunderbird without rebooting does not resolve the problem. The operating system is Windows 7. I have uninstalled and reinstalled Adobe Reader. Any suggestions?