Follow this steps:-
1. Close all the word, excel and power-point instances
2. Open a new instance of word
3. Go to word options
4. In Word Option select Add-Ins, in the 'Manage' dropdown box, choose COM Add-ins and tap on Go button
5. Remove the entry for WordTab and reinstall the office tabs. Thus should ideally work
6. However, In my case it did not work, if same happens with you, delete the WordTab entry again, and click on Add button
7. Browse to the path where office tabs is installed and select the WordTab.dll, this dll should be typically found at: C:\Program Files\OfficeCM\OfficeTab
8. Close the pop-up window for COM Add-Ins, repeat similar steps for your Excel as well, do not forget to select ExcelTab.dll this time
Hope this helps.