Description
If using the Make Diagram Layer tool, there is no diagram with the input network diagram name.
If using the Update Diagram or Delete Diagram tools, there are no diagrams returned with the parameters currently specified for the tool.
If using the Change Diagram Owner tool, the specified diagram names don't exist.
Solution
For the Make Diagram Layer tool, verify that the diagram name set for the Network Diagram Name parameter exists for the input network version.
For the Update Diagram or Delete Diagram tools, verify that there are diagrams based on the specified diagram template name, and with the specified diagram name for the input network version.
For the Change Diagram Owner tool, check the diagram names that may be misspelled.