Application update not working

An application has been installed successfully on my Vista Home Premium 32bit OS.
When I try to update it (the update program is designed to simply replace earlier versions of files) the executable (a .mdb i.e. an Office Access database) reverts to the original version. Other files (text files etc.) update successfully.
This happens even if I uninstall the original version first. That includes checking that all the original files and registry entries have been removed.
If I make a copy of the new executable somewhere other than in its home folder, it presents itself (correctly) as the new version when it starts up. (Of course it does not run properly after that, because it is in the wrong place). Moving that copy into the proper home folder results in it reverting to the original!
How on Earth does that happen?
Anyone know a reason for this, and how it might be overcome, would be appreciated.

Solved this myself.
If User Access Control (UAC) is ON, Vista puts a copy in its VirtualStore during the first installation. All access to the application is then vectored to the copy in VirtualStore. The update, whilst overwriting the original in C:\Program Files, does not overwrite the copy in VirtualStore.
If you turn UAC OFF, Vista forgets about the VirtualStore copy, and the update in C:\Program Files is used.
DavetheBari