Enable/Disable Addin button Greyedout in Internet Explorer

1. Goto Start->run and type Regedit
2. Navigate to the key “HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Internet Explorer\Restrictions

3. In the right pane of this location, look for the DWORD named NoExtensionManagement (REG_DWORD). It must be having the Value data as 1. Double click on the same DWORD to modify its Value data: 0

4. Close the registry and restart the computer.