I have tested this in virtual XP and Win7 machines and usually install4j installer is getting stuck on Uninstalling the previous version when doing an upgrade from 3.6.4 or 3.7.0. You have to manually kill the installer and run it again. Not sure if the can do anything and this is not a install4j bug, but maybe we can look into this.
It happened with 3.7.0 -> 3.8.0 upgrade, but didn't happen when i was installing alpha builds on top, so not sure. I think somebody on the forums mentioned this problem recently.
Went fine with 3.8.1 Alpha -> 3.8.1 final. Closing so far. Will have to check when going to next version.
Have just tried to do 3.7.1 to 3.8.1 in a virtual machine and it got stuck. I think it is struggling when doing an uninstall of differently numbered version maybe.
wroot, is this still an issue? Perhaps updates of install4j have resolved this now?
Looks like new installers doesn't have this issue anymore.