Windows Mobile 6.1 will not keep a VPN connection

We have around 20 HTC Touch Pro mobile phones trying to create a VPN to the main office server. The VPN connects ok, and we can ping the server ip address from the phone. The problem is as soon as IE or Opera is opened to connect to the Intranet, the connection is lost.

Obviously the firewalls are ok to the traffic as RRAS is showing the host is active, and the phone can ping the server - until IE tries to connect the the server name or IP Address.

I'm just about at my wits end with this, so any help would be greatly appreciated.
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Rob WilliamsCommented:
Afraid it is not much help as I have no idea how to change on a mobile unit, but I'll bet it is related to too high an MTU value for the connection.
pauratAuthor Commented:
Thanks for the possible solution. I have now found the registry key required to add the various values and tried values from 1400 to 1500 in multiples on 10. Same problem!

The connection works exactly as expected until IE is opened and pointing to the server IP Address.
Rob WilliamsCommented:
I would try lowering even further as a test, perhaps 1260. 1400 is actually not that low. If there is some improvement, then try to tweak.
Your symptoms are very typical of MTU, though it could very possibly be another issue. When there are MTU issues you can generally make a connection without any problem. It is not until you try pulling data across the VPN that the connection is lost.
Sorry I am not much help other than that.

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pauratAuthor Commented:
Thanks. A point in the right direction and a few tweaks eventually landed me at 1360 MTU as being reasonably stable. Thanks again.
Rob WilliamsCommented:
Thanks paurat. Sorry I couldn't be more helpful with specifics, but glad to hear it is working.
Cheers !
You said glad to hear it is working... but I don't see a solution here.  Does anyone have a solution for this?  I can't keep my HTC touch pro connected either on Windows Mobile 6.1
Rob WilliamsCommented:
ProbablySlackin, one of the features of Experts Exchange I do not like is the ability for the author of the question to post a comment in "accepted Answer" post that only they and the  expert who answered the question can read. Often the final solution is there. I hope I am not breaking any rules, or offending paurat, but they posted the following "...a few tweaks eventually landed me at 1360 MTU as being reasonably stable...."
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