Serialization error - Can't save

Hi All.
I’ve experience some problems saving my project after swapping form 4.20 to 4.21.
After i calculate my light mass a can’t save. It crash around 53% with an error - “Serialization Error: Action Needed - Corrupt data found, please verify your installation”

I’ve reinstall to from scratch and have the same problem.

Any suggestions ?

Thx

Bart