FATAL ERROR !

It is a timeout error.
It means saving the activity take too much time... (more than 30 seconds)

This should not happen (saving an activity should be much shorter than 30 seconds)

Possible causes are :
- you have very important performance issue (that would set projeqtor unusable)
- change leads to sending emails and your smtp server is not properly configured : try and remove smtp host in gloibal paremeters
- you are using Organization budget on very important structure of project : migrate to V6.2 and disable budget in global parameters