SSAS: Class not registered (Exception from HRESULT: 0×80040154 (REGDB_E_CLASSNOTREG))
Today I got this error while trying to browse a cube from the Business Intelligence Development Studio:

The detailed error information told me that the connection failed, because the server actively refused it. Connecting from another pc worked perfectly, so it had to be a problem with my computer.
To solve this problem I needed to reinstall the OWC Component (Microsoft Office 2003 Web Components)
You can find the download here: http://www.microsoft.com/downloads/details.aspx?FamilyID=7287252c-402e-4f72-97a5-e0fd290d4b76&DisplayLang=en
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Thanks a lot! I had the same problem. Reinstallation solved it!