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

Corrupt #741 drawing. 26090000xx.DWG Fatal Error n/a AutoCAD 2014

1) Inserting 3d fittings is very slow & you must hit enter several times to get through the command. Must pick Enter or OK for each fitting. 2) Could also be related to an AutoCAD drawing variable setting.

3dends folder or files missing unhandled exception

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

When trying to insert a 3D fitting via the Fittings Parts Tree, the user gets the error message;

Microsoft .NET Framework
Unhandled Exception has occurred...
Argument 'Key' is not a valid value

When user clicks CONTINUE and tries to use the INSERT button to insert a fitting, another dialog box pops up

INSERT FITTINGS
Unhandled Exception...
Index was out of range.  Must be non-negative and less than the size of the collection.  Parameter name: index

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

eLockViolation