[jdance]

Hi Simon.

I'm no authentication guru, but I'll try my best to help with the basics. To help me (and anyone else who may look at this thread) understand your set up better would you mind providing us with this info?:

On the clients that are failing, have you tried using known good credentials to log on? If so, did this work?

What source are you using for your client authentication certificates?

How are your users set up? (ie are you using firewall accounts, or a third party to authenticate).

Do you have sufficient licenses to cover the new users you are adding?

Thanks
Jason