When you have perform references in a decision tree, you should make sure they are defined on branches above (or after) where they are referenced. Perform subtree references are where the tree ends with a lettered node. You can also detach the subtree where the perform link is defined and then reference the subtree where it had been.
If you see this error in a model which has some of its nodes set using Branch Control, the problem may be that the perform label is defined on a path through the tree that can't be reached. If this is the case, detach the subtree.
Versions: DPL Professional, DPL Enterprise, DPL Portfolio