call to xlfCaller is causing Access Violation

[tc]

I've been writing XLLs for two years and came across a puzzling error.
I created a defined name which takes a user defined function and
another defined name as an input.

When my user defined function calls xlfCaller, it crashes with an
access violation on that exact line when I debug.
Any idea why this error only occurs in the situation above?

I set my Excel to disable multi-threaded calculation to rule that out
as the source of the problem.

[tc]

I am adding additional information. I've spent a few hours debugging
and the problem clearly appears to be due to the xlfCaller call. If I
comment that code out, I'm good. However, I lose functionality by
doing this...