ok, if its the registration of fsx acceleration issue I know it.
It's no an easy one, surprisingly a mater of registry, not written exactly the proper way.
Please do the following before installing acceleration:
Go to the bottom left to the command zone and type 'regedit'
Then 'Edit' in the top bar, look for 'search'
When in 'search' type 'UpperFilters'
After a short while you may see on the right side of the window 'UpperFilters REG_MULTI_SZ XXXX'
XXXX may be different things. Go to the next until you read 'partmgr'
For me it is in the key 53487c23-680f-4585-acc3-1f10d6777e82.
IF YOU READ PartMgr change to partmgr by clicking onto 'UpperFilters'.
Then install Acceleration again. It will ask for registration without anymore trouble.