B1UP: Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG)

You can get a similar error with CRM 4 Outlook, in this case check this article: CO_E_SERVER_EXEC_FAILURE 

Issue

You get this error when starting up SAP Business One:

SystemRuntimeInteropServices.COMException (0x80040154): Retrieving the COM class factory for component with CLSID {632F4591-AA62- 4219-8FB'5-228CF5F60090) failed due to the following error: 80040154 Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG)).

Cause

Usually this error occurs because DI-API has been installed with insufficient privileges (SAP cannot find DI-API from the registry.)

Solution

To fix it, re-install DI-API in Run as administrator mode.

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This issue can also be due to installing an incorrect Add-on version (Example: if you install a SBO10.x add-on on SAP 9.x or vice/versa)