Ipsec VPN connection problems

Hi. I have had Windows Vista for a while and have started encountering problems with my VPN Ipsec connections. I have a few on my computer.

The low down of the problem is this. I can usually connect to a VPN without any trouble, but after a while it suddenly disconnects, and attempts a redial. This 'while' varies between 5 minutes and two hours. Once disconnected, it is impossible to get it to reconnect for a period which goes from a minimum of an hour to a maximum of around 3.

While VPNa is disconnected, I have no problem getting on to the others - however if another (say VPNb) fails, that one is then down for several hours as well, and this in no way affects VPNa's return to function.

I read somewhere that Vista has some kind of timeout feature that might be blocking the VPN from reconnecting once it is down. I have now installed Windows 7 in an attempt to solve the problem, but apparently it has the same feature and I'm getting exactly the same problem.

As my work relies on being able to connect to any VPN at any given time, this is quite an infuriating problem! I am considering going back to XP, which might help.

Oh, and I tried using LLTP but this won't connect as all

I have talked at lenght to my VPN provider but we have exhausted all possibilities and configuration options, and not solved the problem.

If anyone knows what this is down to , and whether it is solvable, I would be incredibily grateful for any information

Many thanks

Sam

I read somewhere that a similar problem was resolved by
activating "IKE and AuthIP IPsec Keying Modules" and "IPsec
Policy Agent" services.
However I checked and these services are both active so that's not the problem