Could not load file or assembly Microsoft.AnalysisServices

After a Service Pack upgrade on a SQL 2005 installation from SP2 to SP4, a job failed with
Executed as user: *****. A .NET Framework error occurred during execution of user-defined routine or aggregate "NameOfUserDefinedStoredProcedure":   System.IO.FileLoadException: Could not load file or assembly 'Microsoft.AnalysisServices, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91' or one of its dependencies. Assembly in host store has a different signature than assembly in GAC. (Exception from HRESULT: 0x80131050)  System.IO.FileLoadException:      at nnn.mmm.fff(String s. The step failed.

Searching the internet gave me the MSDN Forum thread "Framework error:Could not load file or assembly 'Microsoft.AnalysisServices, Version=9.0.242.0". Here I was directed to KB949080 and the handling of assemblies.

A look at the assemblies in the database with
SELECT * FROM sys.assemblies;
and their files with
SELECT * FROM sys.assembly_files;
gave me the details to refresh the assembly registrations with
ALTER ASSEMBLY [Microsoft.AnalysisServices]
FROM N'C:\Program Files (x86)\Microsoft SQL Server\90\SDK\Assemblies\Microsoft.AnalysisServices.DLL';

Now everything is working again.

Reference

MSDN Library: "ALTER ASSEMBLY (Transact-SQL)"
KB949080: "... Assembly in host store has a different signature than assembly in GAC..."