Error code 64 when accessing external websites via TMG 2010

jayfletcher
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I have one user out of a few hundred who is getting error messages when trying to access various websites like google.com.

He is connecting through a TMG 2010 proxy server and keeps getting Error code 64.

64 The specified network name is no longer available.

I can also see that windows update is trying to connect and the same error comes up.

We have tried changing over his PC to a new one, apparently that fixed it for a little while but the issue came back.

He is using IE9 - we cant use anything other than that due to company policy.
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> ...apparently that fixed it for a little while but the issue came back
until he had reinstalled a P2P software?

- Have a look into the TMG alerts, what you can see there.
- Enable logging in TMG - client IP is the IP of the user.

IS the user is connected via WLAN?
Is TMG patched? So SP2 and maybe additional hotfixes?

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Commented:
User is connected via Ethernet,

It is a clean install of windows 7.

TMG is patched as far it it goes. The error messages in TMG logs don't really say much apart from what i already know.
The error code 64 is a generic error which can have a lot of different reasons. At the end, the underlying reason is a connection loss to the target.
As you say that you have a lot of other clients without problems on the same web sites over the same TMG, I would have the imagination, that it is client specific. Means I would exclude reasons which are related to TMG protocols, rules or services connected to Web Filters, or HTTP compression.
The only point what would be a client related TMG reason maybe flood mitigation, that means if a client requests more than the default number of connections, the TMG blocks connections for a defined time, which can cause such outcome.

So, what do we have on the client?
Beside Firewall and virus scanners, which may produce sometimes some nonsense (disable them for testing), I would have all the time the NICs under investigation. Make sure you use the latest drivers and check the settings on the NIC, if there are options enabled, which may conflict with other devices (switches, routers) between the client and TMG. Sometimes on newer NIOCs, there are options enabled, which are not fully supported by the devices (i.e. jumbo frame etc.). Also autonegotiation can make nonsense, you may try to set the NIC to a fixed LAN speed setting, seen this issue a lot of times, mostly fixed by later updates. Or the MTU.
If you have a similar clients with the same NIC, you may compare driver versions (microsoft or manufacturer) as well as the detailed settings.

Even the windows update (if not applied) can sometimes solve such issues.
If I get new laptops, they usually take about 200 updates from MS when they have a preinstalled OS.

Have a look here with maybe some testing instructions:
http://blogs.technet.com/b/yuridiogenes/archive/2008/11/23/error-64-the-specified-network-name-is-no-longer-available-while-browsing-internet-through-isa-server-2006.aspx

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