Can't open .msg attachments
Based on my search on this specific issue, I found out that Google Desktop software may be conflict with Outlook and leads to this problem in some situations. Now, I'd like to suggest you check if Google Desktop was installed on your machine. If so, please remove it and see whether it helps.
Suggestion 1: Remove Google Desktop if it was installed:
1. Click Start, and then click Control Panel.
2. Double click Add or Remove Programs.
3. In the Currently installed programs list, remove Google Desktop if it exists.