VA is not going to suggest "nField" or "szNullValue" in this case, since these parameters are underlined as mistyped symbols.
This does not really help though, since now we need to find out why these parameters are underlined. As a quick and simple test I have just added the following code to a cpp file using VS2005 and VA 1624:
class SQLQueryResult
{
const char* getStringField(int nField, const char* szNullValue="");
};
const char* SQLQueryResult::getStringField( int nField, const char* szNullValue/*=""*/ )
{
banana = 2; // ONLY "banana" is underlined as a mistyped symbol
}
The parameters are correctly recognised for me.