Bryce,
a long and an Int64 are the same thing 64bit signed integer
'long' is just an alias for Int64.
In fact, if we right-click on 'long' and select 'GoToDefinition' the definitionsig' is
// Summary:
// Represents a 64-bit signed integer.
[Serializable]
[ComVisible(true)]
public struct
Int64 : IComparable, IFormattable, IConvertible, IComparable<long>, IEquatable<long>
{ //................
//--------------------------------------------------
another clue :
The acdbEntUpd generates an ERRNO of 5
When the routine returns to AutoCAD, the ERRNO command from the commandLine reports 2.
Command: errno
Enter new value for ERRNO <0>:
Command: entupd
Select an entity to Regen:
adsName is 9158139860942894088
ErrorStatus is OK
api acdbEntUpd_Return is -5001
System variable ERRNO is 5
Complete: System variable ERRNO is 5
Command: errno
Enter new value for ERRNO <2>: