Pat
In your Drainage Run CB17 to DMH15, the first Pipe (DMH11 to DMH12) in the list was connected to a Node DMH11 that does not exist in your Node List - you can see a red Dot on that Run Name flagging that the Run has an issue - if you review each Pipe - the first Pipe has one of the Nodes Blank (unselected) and that is causing your Report to fail - the exception is kind of telling you this but it should be an Error Message you get not an exception - so I will put in a fix for that, however deleting that first pipe allows the report to run no problem on my computer at least
Alan