[Proj] Eric Miller VB Wrapper +nadgrids=

[stevejking]

I'm trying to use Eric Millers VB api with Excel to convert from OSGB36 to
WGS84. I'm sucessfully using

>From "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.999601 +x_0=400000 +y_0=-100000
+ellps=airy +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894
+units=m +no_defs"

To "+proj=longlat +a=6378137 +b=6378137 +datum=WGS84 +no_defs"

But when I try to use a grid shift file for better accuracy I get a DLL
Error 123. I'm using:

>From "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.999601 +x_0=400000 +y_0=-100000
+ellps=airy +nadgrids=C:\Program Files\MapWindow\PROJ_NAD\OSTN02_NTv2.gsb
+units=m +no_defs"
 
*Does anyone know how to use a grid shift / nadgrids file with the VB api
please?*

The Proj_Lib environment variable is set as C:\Program
Files\MapWindow\PROJ_NAD. But I've also tried C:\proj\nad and moving the gsb
file.

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