Server Backup - The media is write-protected (0x80070013)

Hi there,

server backup won't work. I'm trying to backup my data drive but the progress stands still @ 0% for about 0.5h and then quits. Manually copying files to the external drives works however. I am locally logged onto the server.

I already came across this here 

http:// answers.microsoft. com/en-us/windows/forum/windows_vista-files/when-i-tried-to-backup-my-files-i-recieved-an/2f66e3f2-c1b7-44b2-8fc2-8865b45b212c

What did I try until now?

1. disable read-only flag in folder/file properties
2. take ownership with administrator account
3. set "better performance" on policies tab of the device properties

When I check the error log of the backup, I see every single file being rejected for backup, because of the 0x80070013 error.

What is going on here? Please help me out here ...