When opening HydraCAD you get the error;

Exception in hcadmainbase.arx ARX Command

Unhandled Exception c0000027 (c0000027h) at address aca746e7h

Selecting any button from the AutoCAD ribbon creates the fatal error.  Typing or using a toolbar does not create the error. 

AutoCAD Error Aborting

FATAL ERROR: Unhandled e0434352h Exception at 6C6CCF19h

Sometimes followed by;

The program is missing Tool Palettes and Ribbons.
The drawing may briefly open and then crash.

When opening a specific cac file you get this error

Other calc files open fine

No error reported for FSC even when maximum length is clearly exceeded

If you view the FSC properties, it's possible the HoseLength and MaxNumberOfBends values are not set.

When opening HydraCAD, you get this error message or something similar;

AutoCAD Warning

The following shortcuts in the search were invalid and ignored: 

After clicking OK, HydraCAD will open up, albeit very slowly, and almost every step will take an significant amount of time, for example 45 seconds to start a new drawing or to size a pipe

Unable to find Default Profile:

The profile specified as the default AutoCAD profile does not exist.  Open AutoCAD, go to Options...  <<Unnamed Profile>>...

When trying to open HydraKEY, you see the spash screen, but it eventually times out and the application does not open

When trying to open HydraCAD after a recent install, you get this error or one similar to it;

"Missing shortcut", Windows is searching for acad.exe.  To locate the file yourself, click Browse.

AND

Problem with Shortcut - The item 'acad.exe' that this shortcut refers to has been changed or moved, so this shortcut will no longer work properly.

Nearest match based on size, date, and type:

Do you want to fix this shortcut to point to this target or do you just want to delete it?

When opening HydraCAD and trying to open a drawing or a template, you get the error message; 

Also happened when layers were isolated trying to burst objects

'unrecognized version and cannot be read'

No message. Double-clicking a DWG file to launch AutoCAD opens drawing but also starts a new drawing or brings up the Start Menu.

Registry setting missing Opening

Anti-virus real-time scan quarantines files?

Hangs up Opening AutoCAD 2014.

When opening a 3D persistent model drawing, user gets the error and Acad crashes INTERNAL ERROR Dialog box v53.04 + v54.01

AutoCAD MEP 2013 has new swtiches set in shortcut that we don't Opening AutoCAD MEP

A sprinkler head is drawn in space and is not connect to anything. When the drawing is raised a Hydrafitting (cap) is placed on the head. if the purge command is invoked it will cause a fatal error. Fatal error Purge V51

While multiple PDFs are being opened in the PDF viewer, HydraHEADS displays a message box; "There were 'x' PDFs for this sprinkler...". The user clicked OK on the dialog box before the PDF viewer had a chance to open *ALL* the PDFs. Runtime Error dialog box 50.21.4

change in autocad version change in the network change in your connection to the network error 15.570.0 Will not open any

A failure to call the Hydratec security server occured. 

-OR-

Hydratec Security Error

FAILED CALL TO SERVER (to Activate): Could not parse request body into json.

.NET Framework not installed properly Unhandled Exceptio Opening

Multiple flavors of AutoCAD on same machine. The first one gets only partially configured. The paths are set right, but the SMaRT stuff is not configured Opening Multiple