If you start SSMS as administrator on a Windows 7 machine with UAC on, you get the Class not registered error number 80040154 for the TabsStudio.Connect class:
Running SQL Server Management Studio as administrator
Class not registered error 80040154 in SSMS
Tabs Studio installation for SSMS includes registration of the TabsStudio.Connect class for the current user. On a Windows 7 machine with UAC enabled, elevated applications (in this case SSMS running as admin) don’t see registered per-user COM classes (see Per-User COM Registrations and Elevated Processes with UAC on Windows Vista SP1 for more details). I can’t add per-machine TabsStudio.Connect registration to the installer because it runs without admin rights. A workaround is to register TabsStudio.Connect per-machine manually, double clicking a registration file I’ve prepared.
SSMS is a 32-bit application. Running on 32-bit Windows it uses per-machine COM registration from HKEY_LOCAL_MACHINE\Software\Classes\CLSID, on 64-bit Windows – HKEY_LOCAL_MACHINE\Software\Classes\WOW6432node\CLSID (see Registry changes in x64-based versions of Windows Server 2003 and in Windows XP Professional x64 Edition). I’ve prepared two registration files – one for 64-bit Windows and one for 32-bit Windows.
Note that after unsuccessful loading SSMS disables Tabs Studio and doesn’t try to load again on a next start. To enable Tabs Studio startup loading you can reinstall Tabs Studio or change HKCU\Software\Microsoft\Microsoft SQL Server\100\Tools\Shell\Addins\TabsStudio.Connect\LoadBehavior from 0 to 3.
Download links for per-machine TabsStudio.Connect class registration: SSMS on Windows 32-bit, SSMS on Windows 64-bit.
Tabs Studio Blog (organizing Visual Studio document tabs) 