LONG RegQueryValueEx(

HKEY hKey, // handle of key to query
LPTSTR lpValueName, // address of name of value to query
LPDWORD lpReserved, // reserved
LPDWORD lpType, // address of buffer for value type
LPBYTE lpData, // address of data buffer
LPDWORD lpcbData // address of data buffer size
);

у тебя LPDWORD lpType нулю равен