Iphone 4 updated to ios 5.0 and pptp vpn stopped working

Hi!

I've a trouble after updating my iphone 4 to the lastes ios, ver 5.0.

It not connect anymore to any pptp server.

I've tryied to connect to a sbs2003 server and a cisco router, both configured as pptp servers.

If i connect with a pc or other devices, no problems at all.

Before the update all was working fine.

I've tryied to connect via wifi and via gsm/3g network, without any success.

On the server 2003 i get an event from Rasman, event id 20209:

A connection between the VPN server and the VPN client <ip> has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets.

On the log of the cisco router there are a lot of :

001687: Oct 27 11:29:38.840: ppp59 LCP: Timeout: State REQsent

Then the disconnection:

001688: Oct 27 11:29:38.840: ppp59 LCP: O TERMREQ [REQsent] id 10 len 4

001689: Oct 27 11:29:38.840: ppp59 PPP: Phase is TERMINATING

001690: Oct 27 11:29:38.840: ppp59 LCP: State is Listen

001691: Oct 27 11:29:38.840: ppp59 PPP: Sending Acct Event[Down] id[82]

001692: Oct 27 11:29:38.840: ppp59 LCP: State is Closed

001693: Oct 27 11:29:38.840: ppp59 PPP: Phase is DOWN

001694: Oct 27 11:29:38.840: ppp59 PPP: Send Message[Disconnect]

What i can try to check?

Thanks to all!