I found the issue... Norton 360 for some reason quarantined my junk folder. This caused Thunderbird to not display any emails from that point on. I went into Norton just to see if it had run a scan recently and found 2 quarantines. I restored both and voila... Thunderbird works again. I don't know how to remove or delete my question, but since I can't, I figured I'd leave my 'fix' in the reply in case this happens to other users.

An explanation of why you could see the list in the Thread Pane, but when selected showed no content in the 'Message Pane'.

Norton had quarrantined the mbox file containing the email. However, the *.msf index files were still intact, hence the 'Thread Pane' still showed a list. When you selected an email in the list, the index could not locate the actual email because it did not exist thanks to Norton.

If Norton decided something was not correct in that eg: Inbox, junk etc mbox file, it is not able to work out that the single mbox file contains many emails. So does not know which is the offending email.

What you can do to locate a bad email

• Create a folder called 'TB scan' on desktop.
• In Thunderbird, select a folder eg: Inbox
• Select first email
• Highlight all the emails by using 'Ctrl + A' key
• Right click on highlighted emails and select 'Save as'
• Select the 'TB scan' folder on desktop
• Click on 'Select Folder' button.

All highlighted emails will now be saved as individual .eml files in the 'TB scan' folder. Usually, the 'Subject' is used in naming the .eml file.

• Scan the 'TB scan' folder.

Norton can now see each email as an individual file. If there a bad email, it should quarrantine that file and ask what to do with it.

You can then see what files have been quarrantined and know exactly what email it does not like.

• In Thunderbird search for that bad email and delete it.
• Empty the Trash.
• Compact the folder that contained the bad email to ensure it is fully removed.
• You can now delete all the 'saved as' .eml files and empty the 'Recycle bin'
• Then tell Norton to 'fix/delete' the bad quarrantined email.

Repeat this on any mbox file Norton had originally quarrantined.