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

When using Rapid Main or Rapid Line, clicking on the pipe causes a Fatal Error

When clicking the abacus to enter a length, you get this error;

Unhandled exception has occurred in a component in your application.  If you click Continue, the application will ignore this error and attempt to continue.

Index and length must refer to a location within the string.  Parameter name: length

After starting the Move Main command (MMA), and selecting the main to move, the system freezes and the only way to get out is to end task in the Task Manager