[Proj] Proj4-API - pj_init_plus returns a NULL pointer for my ESRI projection string

[Markus Eberhard]

Hi *,
I'm using the Proj4-API. Currently I've problems with the following C++
API call:
     projPJ projPixel = pj_init_plus( "+init=esri:21781" );
The called function returns a NULL pointer.

Strange, the following similar function call works for me
    projPJ projPixel = pj_init_plus( "+init=world:CH1903" );

Thanks for your help.

Markus