Netfolder disappears after Reconfigure

I had created one Netfolder called "Home-Schueler" and granted the Accesss Right to "Lehrer" (Teachers); everything worked fine!
After Reconfiguring Filr (Changing E-Mail-Configuration) and Rebooting, the Netfolder wasn't visible no more?
Then I wanted to recreate the Netfolder with the same name, but this wasn't possible, Error "Folder exists.."
Seems the folder is there but not visible?
How can I fully delete the folder to recreate the new folder with the same name?

Any ideas?
Kind Regards,
Thomas