>>>and here is the C function declaration:
>>>
>>>

BOOL InternetSetOption(
>>>    IN HINTERNET hInternet,
>>>    IN DWORD dwOption,
>>>    IN LPVOID lpBuffer,
>>>    IN DWORD dwBufferLength
>>>);
>>>

>>>
>>
>>Eric, see my reply to the previous question; try allocating a static block and passing the pointer to the block by reference - structures don't like to be moved about.
>>
>
>I will try that whe I get back to that machine.. but where's a struture?

The LPVOID is suspicious - it's either a pointer to a function entrypointy, or to something of indefinite shape and size and type. It's IN, so it shouldn't be getting set, but I'd want to know more about it's construction...