I had problems trying to change Exchange settings in the registry. There was a lot of keys that appeared to be generic that ended up being unique.

I fixed a similar problem by shelling out to the MLCFG32.CPL then using SendKey combinations. You can enumerate the user's name with the macros and I had a very high success rate (I did include a few pauses to be certain tasks had completed and some SetFocus commands)!

Mark