Yeah I do still have the issue
I saw your post there and quoted you in my post in that thread.
I don't see a solution mentioned there?
I'm about to uninstall.
How did you fix it?
Follow Jim's link to update to the latest beta.
Please do note that it is beta and it may still have bugs.
Do you have MC17 and MC18 both installed on the same machine?
When you exit Theater View and it crashes, can you open Task Manager (CTRL-SHIFT-ESC), look on the tab Processes, make sure its sorted on Description (click the collumn header) and scroll down to Media Center ... see if you can find Media Center 18.exe and/or JRService.exe running. Close both processes by selecting them and clicking the End Process button. Make sure they dissapear from the list.
Start Media Center 18 again. If it doesn't automatically go to Theater View, press control-4. Exit Theater View. If you had my issue, it should not crash but return to standard view.
If it still crashes, backup your library to a safe location (File/Library/Backup Library...) and try to completely uninstall both versions, remove all settings and registry entries when asked, and reinstall only MC18. When you choose to remove all settings and registry, you will have to restore your license (unless you're still in trial of course).
Post any questions you might have and myself or someone else will try and help you the best we can.