No connection since possible 21CN - upgrade

[#1]

Hi all,
I had a message on 25/01 to say that the 21CN upgrade was to happen shortly.  I don't think it is a coincidence but since last Thurs (04/02) by router has been unable to connect.  I get a DSL connection, but no Internet.  I have logged a support ticket and am getting slightly mixed messages from tech support.  I was wondering if anyone knows why I might suddenly have no Internet access?  I am using a Linksys WAG54S with the latest firmware (1.01.03).
All the settings are correct and I've been through all kinds of diagnostics with tech support including using the default BT user settings etc.  Interestingly when the router is on Multimode the DSL connects.  On ADSL2/ADSL2+ I don't even get that.
The only thing that isn't set on the router that possibly could be is the default gateway...
I was told to wait 24 hours for the results of a thorough test of the exchange, but according to the support ticket this completed before I was even off the phone! I put the ticket back with tech support but the phone waits are so long and the forum seems quite spritely and active.
Thanks for your help!

[#2]

Ah - this might be relevant: http://community.plus.net/forum/index.php?topic=76508.0
Shouldn't the support staff know about this though!? I've had a ticket open for a couple of days and had two long calls with tech support. Aggh!

[#3]

So is the router set as per that post (only read the first 3 posts) ?

[#4]

Not in front of it at the moment, but I seem to recall that  VPI/VCI 'Autodetect' is enabled.  Will report back later!

[#5]

Turning off VPI/VCI autodetection did indeed fixed the problem. 
Wow - if it wasn't for this forum I would never have guessed that.  And technical support didn't help in the slightest.  If only the support script included more knowledge from the community; when you don't have an internet connection they are your predominant source of technical support!
Cheers!