Thunder Bird help(question from german forum)

Hello!
Recently my Thunderbird Portable mail is no longer down (from GMX), but the following message comes up: "Unable to write the email to the mailbox. Make sure the file system allows you write privileges, and you have enough disk space to copy the mailbox. "
Enough space is available---here I dont understand the second part.
Can anyone help?
bebuquin

Edit: the original from https://portableapps.com/node/13439

I translated the page for him but he said it didnt help, this is why im putting the question here so maybe you all can help find out what is wrong. I tried my best in translating the above, but I know very little german,(my dad taught me some) im more fluent in spanish and english.