How much disk space do you have left on your system drive (propably "C:")?

I have 717 G. free out of 914.

It is more likely that the files are locked by an anti virus program getting in the way. Create an exception from real time scanning in your anti virus program for the Thunderbird profile folder and its children. To try the theory before creating the exception which can be tedious, restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-including-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX]