As usually, the file goes to Downloads; then, when I try to run it I get the message: "The Windows installer service could not be accessed. The Windows installer is not correctly installed. Contact your support personnel."

At the same time, all previously bought games' Windows installer packages run successfully.
I run Windows 7 version.
So, what I supposed to do?
Thank you for advance.
Hauptman Vladimir Repnin von Jahotyn
Klenau Chevaulégers No. 5
Armee v. Österreich