Save Draft Error using Mac Operating System

Hi,
I just upgraded TB 2. X to TB 3.0.1using Mac Operating System and getting this weird error message every time when I compose messages to send using Gmail account. The following error message appears while doing this action. I am unable to save my messages as drafts. It creates a data lost situation for me. Can I resolve this issue with your help? Any assistance would be greatly appreciated. Thanks in advance.

Save Draft Error
Unable to save your message as draft.
Please verify that your Mail & Newsgroups account settings are correct and try again.
