Hard to say without knowing what version of SEP and version of Office. Here's a post a while back that helped me with Outlook:
Try one of these solutions for me:
In Outlook 2007 the Add-ins is located in the Trust Center:
Open the Tools menu in Outlook 2007 ---> Trust Center ---> Add-ins ---> in the "Manage" combo box at the bottom of the page select "Exchange Client Extensions" ---> Click on Go ---> Uncheck "Symantec AntiVirus 10.1" & "Symantec AntiVirus Outlook Protection" ---> Click OK & restart Outlook.
If that does not fix the problem, find and delete all copies of the "Extend.dat" file on the computer. A copy of this file exists for each local user account. Then, restart the computer.
Note: You cannot delete copies of the "Extend.dat" file for other user accounts unless you log on with an account that has local administrator rights.
To find and delete copies of Extend.dat
Close "Outlook" if the program is open.
Confirm that Windows is set to "show hidden and system folders."
On the Windows taskbar, click Start > Search > For Files or Folders.
Under "Search for files or folders named," type the following text:
extend.dat
Click Search Now. Wait for the search to finish.
Delete all copies of the "Extend.dat" file.
Restart the computer.