Mozilla ThunderBird Error "The folder inbox is full"

The whole error message is: "The folder inbox is full, and can't hold any more messages. To make room for more messages, delete any old or unwanted mail and compact the folder".

Follow this steps :

1 - Create a folder called TEMP (can be any name)

2 - Move all messages from Inbox to TEMP

3 - Exit Thunderbird

4 - Go to the LOCAL DIRECTORY folder and erase the 2 files : INBOX and INBOX.MSF

5 - Open thunderbird again

6 - Move ALL MESSAGES from TEMP to Inbox

7 - Erase TEMP folder

8 - DONE