I've seen similar issues to this happening in PowerPoint.
Try unregistering OfficeAV.dll plug-in. This is a Norton antivirus file. Unregistering it won't break anythin.
1. Click Start, point to Find, and then click "Files or Folders".
2. In the Named box, type "officeAV.dll" (without the quotation marks).
3. In the "Look in" box, click the hard disk on which Microsoft Windows
is installed, and then click Find Now.
4. In the list of found files, note the path to the OfficeAV.dll
plug-in.
5. Click Start, and then click Run.
6. In the Open box, type the following line (including the quotation marks), and
then click OK
regsvr32 /u "<path>\officeav.dll" where <path> is the path
you noted in step 4.
7. Click OK when you receive the following message:
DllUnregisterServer in <path>\OfficeAV.dll succeeded.