When trying to insert a valve type fitting from the parts tree, you get the error; 

Still!!! Block ### is missing.  Please insert manually.

However checking the database for the drawing file shows it exists.

When trying to insert a specific fitting, you get the error

Could not add this part to the fitting because of missing endprep

then;

AutoCAD Error Aborting

INTERNAL ERROR: !dbentapi.cpp@719: eNullObjectld

While in your viewport, your riser is visible while in the 2D Wireframe view.  However if you change the Visual Style to Conceptual or Shades of Grey/Shades of Gray, your 3D riser disappears.  You may notice if re-appears if you zoom out.

blue beam loaded on machine (a pdf writer) 3dfittings unhandled exceptio

When clicking the button for the Parts Tree or to Insert via HydraLIST, you get this error

eInvalidContext

Unhandled exception has occurred in a component in your application. If you click Continue, the application will ignore this error and attempt to continue.
elnvalidContext

3D Details (3D Fittings) missing, only the skipoles are showing

When trying to insert a 3D riser object, you get this error;

Call from 'Hcad3Ddetails-fillGridMisc'

DAO Error:

Could not find file

AutoCAD will likely crash out

After setting up a fitting in the Parts Tree then trying to Insert Fitting, you get the Unhandled Exception error below

eLockViolation

After creating a legend for your 3D riser, you use the ILT command to insert a legend tag.  It inserts the tag, but you get the error.  You have to click CONTINUE then repeat the command to place another one.

Unhandled exception has occurred in a component in your application

Arithmetic operation resulted in an overflow

Application does not support just-in-time (JIT)

The "SECTIONPLANE" command caused various pieces of the 3D Details to disappear. You may be able to delete the SECTION PLANE and have the missing items reappear. n/a n/a Hcad v52+