One Share out of five cannot change permissions

Hi everybody. I've got a strange problem with my ReadyNAS NV+ V1:

I am using it in the security-mode "User" and have five shares with different permissions. All of them are using CIFS, some are free for AFP, some for FTP. Now there is one share, on which permissions and protokolls cannot be changed. I try to add FTP by setting it to read only or read/write, click on OK and the wait-wheel starts turning. Once it stops, the page refreshes and the settings are as they were before. The only thing I can do is to activate and deactivate CIFS for this share. All other shares can be edited without problems. Even shares that are created new do not have those problems.

Any ideas? Is there any way of resetting the shares properties? It is full of files, so I don't want to delete it and make it new.