@Teddy welcome to the Rockstor community.
without more details on when this error occurred, I suspect you’re reusing a disk that had another OS/filesystem on it and it has not been properly wiped (including boot sectors, etc.) before being used for Rockstor.
If that’s the case, take a look here:
https://rockstor.com/docs/installation/pre-install-howto.html#wiping-disks
If that’s not the scenario, can you provide some more information on the version you’re using/installing and what you were doing before this error occurred.
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