Hi Jochen,
There is something more sinister going on.
strcpy(test,ca_LastConfigError());
strcpy(sOutput,test);

return;

single stepping through the above executes  you can see that sOutput in the
locals windows has "Oracle error blah blah"
you can then single step to the return OK
when you single step again up into the VB Calling method you get an error
'An unhandled exception of type 'System.ExecutionEngineException' occurred
in Monitor.exe'
Seeing that the VB code and the VC++ code are both inside try catch blocks I
guess the error is somewhere in between the two.
if you can spot the problem  I would be grateful.
Thanks
Bob
*********VB.net  Calling  code START************
Public Function LastConfigErrorMessage() As String

Try

Dim sb As New StringBuilder

sb.Capacity = 256 ' Desperation

sb.Length = 256 ' likewise

LastConfigError(sb)

Return sb.ToString

Catch ex As Exception

WriteErrorLog("DNP3Config.LastConfigErrorMessage " & ex.Message)

End Try

End Function

*************VB Code  END************

*****VC++ code  START***************
void DNPCONFIG_API LastConfigError(char *sOutput)

{

try

{

char test[255];

//strcpy(test, ca_LastConfigError());

//MessageBox(NULL,test,"",0);

strcpy(test,ca_LastConfigError());

//sOutput= ca_LastConfigError();

//MessageBox(NULL,test,"",0);

strcpy(sOutput,test);

//MessageBox(NULL,sOutput,"",0);

return;

}

catch (char * str)

{

char error[255];

strcpy(error,str);

MessageBox(NULL,error,"",0);

}

}

************VC++ CODE END******************