Failed to write a block of data. The repository might be unavailable or corrupted

Hi, I had this error two days ago

 

Failed to write a block of data. The repository might be unavailable or corrupted

I managed to check the repository and rerun the failed backups.

Today I found a back up had lost one of it's drives and failed because it didn't have enough space to back the drive up (4.5TB)

However it has lost all the recovery points for that drive but the space hasn't been returned to the repository.

Anyone know how I can delete the lost recovery chain?

Thanks