Windows Server Backup File system not supported

[Gaz]

I'm trying to use WSB for the first time and when I try to do a full backup (server data, applications, system state) it says "One of the specified source volumes has an invalid format and cannot be protected using Windows Server Backup. Only volumes formatted with NTFS can be protected"

 

There are 2 volumes in storage manager. (OS) (fat32) (C:\) NTFS

 

I get the same error even if I don't select the OS