You just had to have Vista huh?
Client Access did not officially start support for Vista until version 6.1 but from what I can tell your uninstall of 5.2 did not complete properly causing your re-install to fail. My recommendation would be to try and get you hands on a 6.1 version of Client access. Backwards compatibility with 5.2 i5O/S is not very good with Ops Nav but the 5250 session should work fine. Problem, you still need to completely remove V5R2 before you will be allowed to install V6. Unfortunately, I can offer little assistance because V5R2 is not supported with Vista and will cause anomalous behavior if installed, such as you have experienced. Manually removing the software can also be troublesome because of the limited abilities of certain version of vista. If you can’t get your hands on 6.1. I have installed V5R3 and R4 on vista with varying results. Most Problems are encounter with Ops Nav but I would not recommend installing any version on Vista unless using Vista Ultimate with Client access Version 6 release 1.