http://support.microsoft.com/kb/910387
This issue may occur if the Enable IEEE 802.1X authentication for this network check box is selected. If this check box is selected, but there is no server to authenticate against, the connection is disconnected. If you reestablish the wireless network connection, it disconnects again after a short time.
To resolve this issue, use one or more of the following methods in the order that they are provided. After you complete each method, verify that the issue is resolved. If a method does not resolve the issue, go to the next method.
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Method 1: Disable IEEE 802.1X authentication
To disable IEEE 802.1X authentication, follow these steps:
1. Click Start, click Run, type ncpa.cpl, and then click OK.
2. Right-click your wireless network connection, and then click Properties.
3. Click the Wireless Networks tab.
4. Under Preferred networks, click your wireless network, and then click Properties.
5. Click the Authentication tab, click to clear the Enable IEEE 802.1X authentication for this network check box, and then click OK two times.
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Method 2: Remove and re-create the wireless network connection
To remove and re-create the wireless network connection, follow these steps:
1. Click Start, click Run, type ncpa.cpl, and then click OK.
2. Right-click your wireless network connection, and then click Properties.
3. Click the Wireless Networks tab.
4. Under Preferred networks, click your wireless network, and then click Remove.
5. Click View Wireless Networks.
6. Under Network Tasks, click Refresh Network List.
7. Under Choose a wireless network, click the wireless network to which you want to connect, and then click Connect.
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Method 3: Troubleshoot USB wireless network adaptors
If you have a universal serial bus (USB) wireless network adaptor, you may experience problems that are related to the limitations of USB. If you have multiple USB devices, the USB network adaptor may share data bandwidth, power, or both to a level that it causes you to experience the symptoms that are described in the "Symptoms" section. To resolve this issue, try the following suggestions:
* If the computer has more than one USB bus, connect the wireless network adaptor to its own USB bus. Connect other USB devices to a different USB bus. Typically, two USB ports share one USB bus.
* Disconnect any unused or unnecessary USB devices.
* Use a powered USB hub to connect the network adaptor to your computer.