When installing Probate Plus if you get a message that Probate Plus is open on your PC then make sure that you close Probate Plus prior to installing any new version.
If Probate Plus is not installed or running then it may be that an application sharing the same application name (prowin32.exe) may be running on your PC and the setup program is detecting this application as Probate Plus.
Try closing any running applications then retry installing Probate Plus (this is recommended when installing anyway). A known application from SOS (Solicitors Own Software) also shares the prowin32.exe application name so if you're running SOS you may come across this issue.
Also, you can use the Windows task manager to look for any applications named prowin32.exe that may be running to give you an idea of the application that is causing conflict.