Is this a folder you created in 'Local Folders' account? What is the name of the folder?

Do you use Global Inbox(Local Folders) for a POP mail account?

If you delete the folder, does it go to the 'Deleted' folder in 'Local Folders'? If you then right click on the 'Deleted/Trash' folder and select 'Empty Deleted' does it reappear?

The folder was created in "Local Folders".

Yes, I use a global inbox for a POP mail account.

There are actually two file folders in local folders with the exact same name, that when I delete them, one goes to trash and one stays in the "local folders", it will not delete. The one that goes to trash deletes when I empty trash, but then reappears with the other folder in "local folders". Crazy huh?? I have done this several times always resulting with the reappearance of both file folders.

What is it called?

1549 Raytheon Foam Castings Quotation 060315 RFQ WF1416835 f10773d1

I have tried renaming it multiple times but it keeps reappearing. The last 8 characters appeared on it's own.

That's the name of a folder? That will be made into a filename in your file system. Given its location, is it possible or likely that the total pathname length exceeds the limit of the operating system?

For instance: http://windows.microsoft.com/en-gb/windows/file-names-extensions-faq#1TC=windows-7

That's not to mention any other limits that might be inherent in the way Thunderbird uses filenames internally.

In your position, I'd explore the Thunderbird profile and check pathnames as they appear in the file manager. You should be able to delete any unwanted folders there too.