Extra line of input was entered into the VPUMP.DAT file found here; \HES\HydraCAD\Ver50\Programs\3DFTGS Unhandled Exception Insert Pump n/a

No error, pump just doesn't insert 

Revit could not complete the external command... Name contains illegal characters

Discharge and or Suction inputs were typed in and not entered via the pull down. input new pump

Pump is in water supply but no reference point PI

Command Failure for External Command... ...System.IO.DirectoryNotFoundException

Revit could not complete the external command.... Details: Name must be unique... At HCAD_Revit_Tools.CAD3.Insert_Pump.Go

Runtime Error 62: Input past end of file

After running an update to 50.54, user is getting this error when trying to add a fitting by right-clicking the fittings cell, a dialog box pops up saying,  May happen with Pipe Schedule and adding a Pump as well.

File to load paths and Dirs.(AND STRING CONVERSION)
CommandLine... yadda yadda yadda

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 trying to run the calculation, you get the message, 

"The system flow demand of ### exceeds the maximum rated flow as indicated in the Pump Curve for the pump with the inlet of PI and outlet of PO.  The calculation will not continue"

But your flow is a very large number

System seems to hang at this step, but eventually shows the error;

Hydraulic Calculation - The system flow demand of ####.## exceeds the maximum rated flow as indicated in the Pump Curve for the pump with the inlet of PI and outlet of PO.

The calculation will not continue Calculation failed for an unknown reason

May not be 1a.3 or 2.3, could be anywhere along here.

When inserting a listing tag on a pipe, you get the error, "Invalid color number"

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

When trying to insert a riser nipple/vertical pipe, you get a FATAL ERROR:  Unhandled Access Violation. 592A00h or 8B2A00h

Error when attempting to make a fluid delivery time file...

When starting the AutoCALC process, you get this error;

Could not find fitting match for Pump Only/Test Point Please check!!

You also see an Accessing Database window with a partial green progress bar.

No Operating Heads of Flows Found!!  Please check...

During the install of HydraCAD, you get an error, "Setup Needs the Next Disk, Please insert disk 1 that contains the file data2cab"

No Ribbons / only the HydraCAD Ribbon appears, and no commands work.
Revit could not complete the external command. Could not load file or assembly. The system cannot find the specified file. 

Inserting a pipe dimension (pipex) places it at the end of the pipe, including its center grip or not even on the pipe at all

See solution #3 if the PIPEX is not on the pipe