To solve the previous problem I first uninstalled LoadUI PRO v2.5.2. Then I started LoadUI PRO v2.5.1 (it was still installed) and tried to open the previous (v2.5.1) project files. The result was that the 2.5.1 GUI would only display a blank white screen. When I exited the program I got the error dialog box that says: “A problem occurred during startup and LoadUI needs to restart – Restart/Quit”. I tried restart and that did not help so next time I tried Quit and that did not help. i.e. still blank white screen on next attempt to run it.
So I have tried uninstalling everything (i.e. free version, version 2.5.1, version 2.5.2 and LoadUI Agent) and rebooting and then only reinstalling 2.5.1 and still just a blank white GUI appears with that same error dialog box.
To finally fix this I found that I had to also delete the folder C:\users\"name"\.loadui and then restart LoadUI 2.5.1 again and then v2.5.1 recreated the .loadui folder and it works again (i.e. no white screen)
Make a copy of your .loadUI directory before you do this so you can reload your previous project files and other work.