Hi,
The installer checks whether there was any installation on the machine before. You can't install "eval" on a machine where there was "free" before and vice versa.
Would you be able to install either the free or eval (functional for 14 days) on a clean machine? A small VM should be OK for testing purposes (except for performance).
If you use the "eval" version, you will definitely receive support.
Regards,
Jiri