Revit could not complete the external command     System.NullReferenceException

ERROR: No fittings were found on the selected pipe

Command Failure for External Command... System.NullReferenceException

When trying to open a drawing file, you get this error; 

DAO Server - Error DBOpen4

Call from 'hcad_fignames'.

Path:'C:\HES\HydraCAD\Ver50\AutoListElements\Data\Setup\MdbTRANS.mdb'

DAO Error:  Unrecognized database format

C:\HES\HydraCAD\Ver50\AutoListElements\Data\Setup\mdbtrans.mdb'

When you click OK, AutoCAD crashes out

When plotting to Bluebeam document, some HydraCAD drawing entities show up blacked out.

AutoCAD view;

PDF generated by Bluebeam;

After clicking the Start AutoCALCs (SAL command) button but BEFORE the AutoCALC Setup window, you get the 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.

The input string '1◆' was not in a correct format.

 Line / Main tags are blocking items behind the text / tags are not transparent

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

When running the "FSC Setup" to "Create FSC Definition". 
Upon finishing the block definition, the block definition is missing a crucial property for "Hydraulic equivalent length is referenced by:". This field will show blank or the default generic text and did not include the HydraCALC pipe/fitting reference information.

There is a missing HydraCALC "ImportExport" directory.

Default line text:
`Hydraulic equivalent length is referenced by: shortname with length number - longname Listing: FM`

The diameter tag HANDLE is 0000 this number is used to determin if the pipe is sloped - yielding an incorrect pipe length. Move Line / Move Main make the diameter tag HANDLE be 0000

Revit could not complete the external command... The 3D view ownerDBViewId is not locked

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

Printing a calc shows this error in HydraVIEW;

File not found Runtime Error 53

After printing your data in HydraLIST, when HydraVIEW opens you attempt to change the default printer. 

You get an error "Page Setup - Unknown filetype found 'HLTF'"

Edit Remote Area dialog box is cut off (Can also happen to the main HydraCALC for Revit Setup dialog box)

When opening HydraCAD, you get this error

Unhandled Exception...DAO32Server...

When trying to insert a Sprinkler Head Schedule (SHS command), after viewing the setup dialog box, then selecting sprinkler heads, when asked to select a location for the guide, you get the error;

Please pick start point for schedule

Error: bad argument value: non-negative: -1

Keyboard alias "SAC"

After clicking OK in the AutoCalc Setup window and just before the process begins, you get the following error messages;

Problem updating your Hcad_env.ini file.  /n Will try to rebuild file. /r Pick OK then Restart AutoCALC

Your Hcad_env.ini file is possibly corrupted.  This calc will not continue

After running an Autolist, in HydraLIST and the LINES tab you have a listing tag ID called RM

No error occurs but HydraCAD will not properly load and Hcad commands do not work.  

A quick test is to select the drop menu [File|New], select the template file 'HydraCAD Imperial Default.dwt'.  

The Drawing Setup window should appear but it does not, it loads straight into a blank drawing.

This is what you should see (press F2 to review the text window);

Instead you only see;

HCAD_ADS r4 functions Loaded.

AutoCAD menu utilities loaded.
Requires an integer between 0 and 32767.

3dFitting registry keys found

Requires an integer between 0 and 32767.