If you have 5.1 installed on the same computer I do not expect you to get 5.0 Isogen to work. Up to now only the following combinations work:

- 5.0 on its own
- 5.1 works if 5.0 is installed first and not removed (but not on all computers)

5.1 isogen will not work on its own. If you install 5.0 then 5.1 and then remove 5.0 Isogen doesn't work anymore. Removal of 5.0 can also break some other programs. If you installed first 5.1 you have to install 5.0 and then repair 5.1 installation.

In summary you cannot uninstall 5.0 ever.

A bit of a mess.