In MS Office 2010 programs, this error occurs when u open a file type that is blocked by File Block settings in the Trust Center. To come out from this try out the follow steps:
1. Click the File tab.
2. Under Help, click Options.
3. Click Trust Center, and then click Trust Center Settings.
4. In the Trust Center, click File Block Settings.
For more info, may link to : http://support.microsoft.com/?kbid=829072 (though it is related to 2003, but it might be helpful)
Hope it helps u !