Hi Frank,
What's the KB # of your SP2 file ? mine is named MicrosoftDynamicsGP11-KB2435566-ENU.msi from the Updates folder in the GP2010R2 installation package (downloaded from the customer source). This worked perfectly on the server and client side. My current version is 11.00.1752.
However, I was surprised when doing the upgrade that the GP2010 client could not be installed over the existing GP10SP5 folder and I had to select a new folder. This is a little bit annoying since I have plenty of 3rd party products and Forecaster/FRx that I need to migrate manually and change all the path definitions...
One thing that I found out that in one of the RepXXX.txt files that are used as input, for one module there was one upgrade path missing (i.e. ['11.0.1053' to '11.0.1247'] ### Do nothing here. Just needs to be in here.). I added manually the section by copying it from another one and the upgrade worked just fine (I think that was during the process of upgrading the modified forms & reports).
Hope this helps and good luck,
Beat