User created two viewports in a layout tab of a 3D pipe drawn in the 3d_details layer.  One of the viewports plotted fine but the other didn't show the pipe at all.

AutoCAD view of viewports, note the selected pipe is the same in both drawings;

Post plot, PDF View; note all of the 3D Details pipe is missing from the right viewport

possible annotative scale issue.

bad head definition, in this case Head4

Error occurs when using some commands.

Autodesk has just released AutoCAD 2026.1.2 - and it breaks HydraCAD. It includes a major programming change by Autodesk that will require a lot of work and a large update by us. That update is being worked on right now, along with a version of HydraCAD for AutoCAD 2027. Both are now affected by essentially the same programming change.

BinaryFormatter serialization and deserialization are disabled within this application. See  https://aka.ms/binaryformatter for more information.

Other commands with this error;

Sprinkler Layout dialog (SL command)

Have AutoCAD select a group of pipe dimension blocks with a specific diameter or length. 

In this example I want to find and delete all diameters with a ?" as its value.

When trying to size a pipe, the units show up as millimetres/millimeters (mm) instead of inches OR the values for half show up as a backslash

When attempting to insert a pipe dimension you get the error "Invalid option keyword"

And the command prompt says "Enter an UNDO control option" with the dialog showing your choices

When attempting to insert a cap, it draws the pipe and dimensions it, but it doesn't insert a cap.

However if you draw a test pipe elsewhere, it successfully inserts the cap for you

A second copy of PIPEX blocks (SPRKDATA layer) appears on the drawing when using NWCOUT