I am also having this problem since upgrading to the latest version, please see linked screengrabs:-
I removed old extension first, installed new version and have also deleted the MacFileCache.dat file, but still no joy.
I also urgently need to send out some emails, is there a quick fix for this. Or should I try reverting back to the previous version?
UPDATE: I have uninstalled 3.07 and re-installed 3.06 and all seems to be fine again.