Error occured when connect to MySql Databse in Dreamweaver

Hello! I met a problem when connect to Mysql Databse in Dreamweaver

Details:

My Php Environment: Php 5.2.2+ MySql 5.0.4 + IIS 6.0 + DW IDE + WinXP SP2,

All necessary sevice started(Actually I have never stopped any Windows service).

Php installed (IIS + CGI) and tested successfully in DW

MySql Installtion(Typical Install with extensions ) and configuration are both OK.
Configuration Details:
For configuration type, select Detailed Configuration.
For server type, select Developer Machine
For database usage, select Non-Transactional Database Only.
For the number of concurrent connections, select Decision Support(DSS)/OLAP.
For networking options, accept the default settings.
For the default character set, accept the default setting.
For the Windows options, select both options – Install As Windows Service, and Include Bin Directory in Windows Path.
For security options, enter a root password and confirmed.

And then I Created a database "mydb" with 3 tables inside by "MySql Command Line Client",
...... (Approach Obmit here)
Open "MySql Command Line Client":
Type >mysql Show Database mydb;
Show a list with 3 tables(Created Successfully)

Then In DW,
Open my Php webpage,
Then from Database Panel>MySql Connection,
Connect Name:myconn
Mysql Server:localhost
Username:root (Right)
Password:111111(Right)
Database:mydb

Click "OK", but when DW tried to connect to MySql database, then DW popuped an alert dialog says "HTTP Error Code 502 Bad Gateway",
I don't know what this mean and how to solve this problem, hope any PHP and DW expert can help me, thank you very much.