To add what the others have said
You need to tell Micro Code Studio where Mpasm is located.
There is a pull down menu on MCS "view". I think it say's compiler/assembler options.
The same place you select PM or MPASM. There are two buttons "find manually" or "auto"
Try auto first it will scan your pc and tell MCS were mpasm and the inc files are
located. After this it will act like your old installation. None of this has to do with
64bit pc.