Analysis Services - Provider cannot be found

I've got a big problem with the Analysis Services.
I have a SQL Server 2000 SP3 and the Analysis Services SP3 running. The SQL Server has no problems.
When I try to browse the Data of any cube, the following error message occurs:
"Provider cannot be found. It may not be properly installed." When I try to browse other cubes after this, the error message "unknown error" occurs.
The databases, on which the cubes are based are both Access2k and SQL Server 2k. The error even appears at the test cubes from Microsoft, so it cannot be simply a problem of the database.

Much thx for your answers.Try to restart the services on the machine.|||That would be an easy solution. I tried it at first. :-)
It didn't change anything.|||Are you trying to browse from WINXP? If so, you'll need to install sp3 for analysis services on the client.|||I could solve the problem. I had an error when installing sp3 for analysis services on the server. I didn't take notice of it. Later I checked the Version number and recognized, that sp3 was not installed. I installed sp3 again and then it works.

greets,
Stefan