MATLAB - fastRCNNObjectDetector issues when complied into a .dll

I have a trained CNN, which comprises a detector.mat file with the parameters/regions of interest definitions etc. contained within it.

When running the detector code in the MATLAB IDE itself, I am getting excellent results.

However, my problems began when I have tried to compile the code into a .NET DLL.

Passing in the exact same parameters (detector.mat file and path to the same .jpg image) I get an error:

MWMCR::EvaluateFunction error ...
Struct contents reference from a non-struct array object.
Error in = > MyDetectionRoutine.m at line 8

... Matlab M-code StackTrace ...
  at
file
C:\Development\toolbox\vision\vision\fastRCNNObjectDetector.m, name 
fastRCNNObjectDetector.parseDetectinputs, line 755

I can't work out why it doesn't work for me as a compiled .dll.

Any suggestions would be gratefully received.