If you run Virtual TI 2.5 beta 5 under Windows 7, it fails with an error dialog which says "Failed to set data for 'LastEmuVersion'". A simple workaround is always running Virtual TI as Administrator, but that gets annoying.
The error means that Virtual TI was unable to save settings in the registry. It attempts to save settings under HKEY_LOCAL_MACHINE\SOFTWARE\ACZ, and it is not allowed to write there. Instead, it should be saving them under HKEY_CURRENT_USER\Software\ACZ. Normally, Windows 7 registry virtualization would automatically fix this problem by redirecting writes HKEY_CURRENT_USER\Software\Classes\VirtualStore\MACHINE\SOFTWARE\ACZ, but something goes wrong.
To fix the problem, open regedit and grant yourself write access to KEY_CURRENT_USER\Software\Classes\VirtualStore\MACHINE\SOFTWARE\ACZ and all of its child objects. If the key doesn't exist, create it.