I was having this same problem of not being able to open email attachments of other emails for approx the last 2 weeks. My contracted IT guy gave me several suggestions including running the "repair" function on Outlook from within "Settings>Control Panel>Add/Remove Programs" - none of which worked. When I searched MS and the web for possible solutions, I came upon this forum and the advice of disabling "Google Desktop Search". Then it dawned on me... about 2 weeks ago, I noticed “Google Desktop Search” on my lower taskbar. I didn’t know how it came to be there and didn’t knowingly install it. So I went to "Programs>Google>Uninstall Google Desktop" and uninstalled it. After rebooting, I can now open my email attachments again. I wasn't using Google Desktop Search, so it's no loss.
Thanks very much, Kathleen Orland, for helping me figure out and solve this very annoying issue. I hope this helps someone else.
Best regards, Tony Swatek
http://www.scrapyourtrip.com