While importing an AutoCAD model into Revit, you get errors listed below;

Revit could not complete external command... System.NullReferenceException

There are identical instances in the same place.. This will result in double counting in schedules. 

When attempting to create a Flexible Connection you get these errors;

Then this;

Could not find file FSC-INSERTDEFLINE.txt

When starting the process to insert a Flexible Sprinkler Connection, you get the error message above;

An error occurred reading the FSC-Selections.txt

Double-clicking your HydraCALC icon makes nothing happen.  You do not see HydraCALC open onscreen nor on your taskbar.  HydraCALC does not open other than in the task manager.

If you open your task manager and see the app "Hyd_prog.exe" open but not on your taskbar, then the application is stuck in purgatory.

Another possibility may be that it's on the taskbar but not on your screen.  That means it's open but offscreen. 

See this HydraCARD to fix that issue;  HydraCARD 565 only AFTER you've checked on the solution below.

When inserting a VP, the text shows double white text, not white and magenta.  Using the CEL or CUL command still shows the double text

The setup was unable to automatically close all requested applications. Please ensure that the applications holding files in use are closed before continuing with the installation.

Files in Use. Some files that need to be updated are currently in use.

Revit could not complete the external command.  Revit encountered a System.DllNotFoundException: Unable to load DLL 'HydraLibRVT.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

Error 98. Access Denied to System. This occurs when opening any hydratec product using your Hardware lock.

After buiding your 3D risers, raising to 3D, exporting to a Persistent Model and Navisworks successfully, your 3D riser is missing, with the exception of the skipoles

Your layers are on and the 3D_DETAIL layer is present, unlocked, thawed and visible, you just can't see the pipe and fittings.  The one customer reporting this said they disappear if the drawing is closed then re-opened.  They'll be visible in viewports as well, just not in 2D view.

See this related HydraCARD also;  https://hydracards.hydratecinc.com/cards/card-1144

You are not currently authorized to use this Hydratec Product.   Lack of authorization.

When making a 3D model, the sprinkler heads appear on the floor.

Authorization Updater Failed.

Failed to Renew. Answer from server was incorrect.

Failed to Open Mail program on local machine.  You don't have a default mail program set on your machine or are using only online mail.

The Lock Code '' is not properly formatted. Ensure this is the code received from Hydratec in response to the above 'Lock Extension Number'.

The Activation Code 'xxxxxxx' is not properly formatted. Ensure that it matches the activation code provided by Hydratec in a recent email.

Failed to open Hydrakey.

Cannot get latest Hydrakey update information.