VB - making API calls

I am using API calls which modify Registry with the following functions,
RegSetValueEx,
RegQueryValueEx,
RegOpenKeyEx,
RegCloseKey
I am working on VB 6.0 in 95 platform and the program works fine.
When I run the exe on Windows NT i can open the key and view the values but not update the values.

Can anybody help me. My project is stuck up because of this.

make sure you specify the correct value for the samDesired in your RegOpenKeyEx call (KEY_WRITE).
Also, check the return code of all API calls and call FormatMessage to get a readable explanation of the error.