Hydratec Inc.

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Revit Based HydraLIST (Ribbon/Toolbar/Location)

Button: Create Stocklist Error Type: Revit could not complete the external command.


Revit could not complete the external command     System.NullReferenceException




HydraLIST Setup may not have been run yet. 


Be sure to run HydraLIST setup and try creating stocklist again, this may resolve the issue. 


Most likely cause is a bad Primary listing tag

Pick Show Tag Locations from the HydraLIST Ribbon


If there is a bad listing tag you will get this error



Follow the instructions to find the error by looking for the ERROR message in the view, or opening the schedule.

When the pipe is located, use the Tag Setup button to Read then Update the tag. Be sure to pick the correct end of the pipe where the tag should start.


Pipes identified as primary tag locations contain incorrect information identifying the fitting at the start end of that pipe.  This can occur if the model is altered significantly after it is tagged for listing.  The tag information contained in Additional Stocklist Information includes the obhect id of the fitting at the satrt end of the pipe (when it was tagged).  If the model is later changed and that fittting is deleted and recreated, it will have a different object id and the one in the pipe property will be broken.  Solution one above provides automated procedures to report and or display those brokenen links.  If that doesn't work for some reason, then the solution here provides guidence for avoiding the problem instead of fixing it.


A simple alternate is:

  • Create a view cropped to just what you want to tag / list
  • Use delete primary tags to delete all listing tags in that view
  • Start tagging your system

If there are still some mismatched primary tags in your project, they may give you trouble later if you try to do more listing in those areas but the trick above could be reapplied to that area later

Updated: Sept. 20, 2022, 12:44 a.m. Created: Feb. 28, 2020, 7:25 p.m.