Call to functions in external DLL fails

I am loading a DLL along with its include file. Libfunctions lists all the functions properly. Call to the functions fail with Method not found. I verified the list of exported functions (using other tools) and they are valid.

Here is the code:

%Load Library
if not(libisloaded('Trialware'))
[notfound,warnings] = loadlibrary('Trialware.dll','TrialWare.h')
end

%Call function .
key='1289794832985798769878469056709379';

handle=double(0)
libfunctions('Trialware')
ret= calllib('Trialware','ReadSettingsRetStr',key, handle)
%print ret
ret= calllib('Trialware','DisplayRegistrationStr',key, handle)
%Clean up.
unloadlibrary lib

Does anyone know what is the issue? All helps appreciated.