Ok, try this:
around line 659 of inc_functions.asp you'll find this function:
function getMemberID(fUser_Name)
'## Forum_SQL
strSql = "SELECT " & strMemberTablePrefix & "MEMBERS.MEMBER_ID "
strSql = strSql & " FROM " & strMemberTablePrefix & "MEMBERS "
strSql = strSql & " WHERE M_NAME = '" & fUser_Name & "'"
rsGetMemberID = my_Conn.Execute(strSql)
getMemberID = rsGetMemberID("MEMBER_ID")
end function
Change the red highlighted line above to this:
strSql = strSql & " WHERE " & strDBNTSQLName & " = '" & fUser_Name & "'"
See if that fixes it.