When trying to save a project I get “IOException during serialization”, this seems to happen if I try to save or copy one screen but not any others. The screen has some “month view”'s and a report but not a lot else. There was nothing wrong before upgrading to 7.3 and I am at a loss, I have attached the full error code. 
Error.txt (4.32 KB)
This is a known issue that has been fixed for 7.3.2. You can download the beta today, the official release is scheduled for the 28th.