I created an alert policy without issue. Make sure the name you are using is unique. If you provide details about what you are doing then someone may be able to reproduce the issue.

Attached you will find what i am trying to do. Simple Alert Rule when Critical or Error event occure, the i want to get an email. Nothing special. But when i try to save it i got an nothing saying error.

Name is unique.

I am having the exact same issue. I had not tried to create an e-mail alert policy before upgrading to 3.3.1.12 today, though, so I am not sure if this is a new issue. My guess is that it is, because this is the only thread I found online with this issue. 

Your time interval is not displaying the same way mine is, make sure you clear browser cache/temp files. I tried to recreate your settings, I had no issue creating another alert policy.

OMEnt alert policy

I tried chrome incognito and now it works. thank you.

strange that some cached thing blocked the creation of that policy.