1603.Error installing Windows Installer engine

Hi TechyV!
I am getting an error message when I try to install the Media Portal Software on my desktop PC.
I already have Microsoft SQL Server and Microsoft visual C++ Redistributable package. Did I miss anything?
What previously installed programs might be causing the trouble?
Please help,
Thanks a lot.

InstallShield
1603.Error installing Windows Installer engine. A
file which needs to be replaced may be held in use.
Close all applications and try again.
OK
