[quote user="D C"]I am accessing the API through .NET linked to Mathematica ...[/quote]
Impressive!
However, I suggest that you initially write your code in MicroStation VBA, using the MicroStation VBA IDE. Once that's working you can port it to another environment.
[quote user="D C"]Here is a modification of the relevant parts of the "Flattening Elements" example for Helix in the VBA docs that resembles how I am using it[/quote]
Code that resembles something else is not the code you're attempting to debug. Nor is it something that we can sensibly analyse and comment on.
[quote user="D C"]my code wouldn't be of much use to most[/quote]
Well, if we can't attempt to run your code in order to test it, then it's definitely of little use.
Please write some VBA, test it, and report back here if the helix error persists.