trouble installing RTW Alexander download

I downloaded RTW Alexander for my son but when I try to install it I get a message stating...."no prior installation of RTWfound. The installation program will now terminate."

I have re-installed RTW and RTW BI
I have downloaded and run the 1.3, 1.5 and 1.6 patches but still no good.

Does anyone know what the problem could be?

Thanks very much

Turkle:help:

have you made sure that the installation path is pointing to the right place, ie where you have installed RomeTW?

Is your drive partitioned, anything like that?