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)

Using HydraCAD buttons cause errors like Loading Shared Parameters for Pipes Failed....

Windows 11 Smart App Control is blocking HCADLoader.arx because Windows says it cannot confirm who published the file. HydraCAD then gives Security Error and fails to load its functions. 

When setting up a new head, the dialog that displays the head symbols to be selected appears, is empty, and then drawing crashes,

During the HydraCAD install, you get an error saying, "InstallShield Wizard - Unable to find HKEY_CLASSES_ROOT\.DWG registry key.  You may need to repair AutoCAD or reinstall it

1. Missing profile 2. Bad registry entry 3. User does not have Admin privileges Unable to find profile Installation Acad 2015~

When raising to 3D, you get the error message, "Error loading the Error GUI has occurred.  How ironic."

The drawing will raise to 3D, but you won't see the error dialog window.

Trying the Show Model Errors command (SME) produces the same error

Trying the DDL command gives the error; 

Usage: (acad_strlsort <list of strings>)

Error bad argument type: consp nil

When importing a Persistent Model into Revizto, none of the riser nipples are visible

During the install of HydraCAD V56/57/58, the user is greeted with the message below.  Following the both sets of instructions of opening and closing AutoCAD, and running a repair of AutoCAD do not make a difference.  You'll still get the error message.

V56 = R23.X
V57 = R24.X
V58 = R25.X

V57 install will say;

Neither AutoCAD 2021, 2022, 2023 nor 2024 found (missing registry key:

HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R24.X).

Please install it before re-running this install