I was using Jasperserver in different browser tabs and did many changes. Suddenly, I got an error like ‘Tree load error‘. To fix this, you need to clean your computer with a program like CCleaner. This was the only solution that worked for me. Even restarting the server didn’t help.
To download CCleaner, go to https://www.piriform.com/ccleaner. I hope this works for you too. Enjoy!