Thank you for your forum post and sorry that you have encountered a problem. I personally have never seen this particular install/uninstall error.
I recommend that you either disable or completely remove the SQL Backup resource in the Cluster Manager prior to attempting the uninstall.
Once the resource is disabled or removed, log-in to each node in turn. Ensure that there is not a SQL Backup task in progress. From the Control Panel ->Programs ->Programs and Features ->Locate the entry for SQL Backup 7 (Server Components) or for a named instance SQL Backup 7 - <instance name> (Server Components) and select the option to remove.