I've had a simliar problem before, the best solution is to shut the VM down, remove it from the inventory (Right Click > "Remove from Inventory") and then go into the datastore it was on and find the vmx file, then right click that and "Add to inventory", following the steps to select folders, resource pools etc.
Voila! No longer managed by SRM
Richard Kuczma
Regards
Richard Kuczma