Finally everything works smooth.
If I had used a Server 2003 compatible hardware in the first place, upgrade would have been easy.
But, as I now read here: http://na.blackberry.com/eng/support...er_april09.pdf
It should not be neccessary to upgrade to windows 2003 for a BES 5.0 installation. Had I known this before, I had installed 5.0 in windows 2000 Server, no need to upgrade to 2003 !
My information about the upgrade to 5.0 and the system requirements are from here: http://na.blackberry.com/eng/deliver...rade_Guide.pdf
There is NOT A SINGLE WORD about Windows 2000 Server (with the exeption of the Clients for Web Desktop Manager). Everything here tells me: Minimum requirements 2003 Server, Exchange 2003
I double checked this by searching the pdf for the word "2000".
Documentation about a product should be consistent across different documents. You cannot expect I read all availible papers before deciding what to do.