SQL Backup uses the SQL Server Virtual Device Interface (VDI) to back up and restore databases.
In your case, the VDI is raising error 80070008, which is undocumented in the VDI specification. Hence, I can't tell exactly what went wrong. In most cases, SQL Server will add an entry to the Windows event log providing more details about the VDI error e.g.
You could also try looking in the SQL Server error log to see if any errors were recorded.