Hi,
I just tried the new beta of Mp3tag: 2.39m.
Everything was fine until I had the following occurence:
When I want to delete an action without any name (by clicking right on title -> Converter -> Actions) it says an exception was raised in the C++ file mtactionsselectdlg.cpp at line 161.
Before I wanted to delete it I unchecked it.
I can delete it manually via Windows Explorer but now the error is raised every time I try to access that menu. 
Error log is attached (although it doesn't say anything else that's important)