VPN connection on Windows Vista no longer works.

Hello,

One of our remote users running Vista Home Premium has had a VPN connection
to our office for several months, working with no issues whatsoever.

However, recently (within the last month) this VPN connection has stopped
working: that is to say the connection attempt times out and the user gets an
error message to say that it has failed. Also, our router does not record any
attempt made by the user's PC to connect to our network - it's almost as if
the Vista PC doesn't even try to connect.

We have tried connecting via VPN on another Vista Home Premium machine and
this works. We have tried connecting using the username and password of the
user on a different PC, which also works. The user has also successfully
connected via his ISP to the company network using another PC which he has
and which runs Windows 2000. We have tried deleting and re-creating the VPN
connection and this makes no difference either.

Are there any recently-released Vista updates that could potentially have
caused this problem? The baffling thing is that the VPN worked happily for
months and then overnight stopped working, despite the fact that no settings
were changed or interfered with and no other software was installed around
this time either. Any suggestions or solutions would be appreciated.

Richard Goodchild.