We have a large number of 1240ag Aironet access points which have been working just fine with IOS 12.3(8)JEA2 and we are able to establish PPTP connections to our Cisco VPN 300 Concentrator.
However, when I upgrade to 12.4 (tried 12.4(3g)JA1 and 12.4(10b)JA) the PPTP no longer works. All other communication is fine and I can establish an IPSEC VPN back to the VPN concentrator.
A packet capture shows the PPTP control packets are being exchanged fine, but the GRE packets seem to be re-sent from both sides continuously until the VPN client times out while showing "Verifying username and password". The concentrator see's a tunnel establishment request, but the GRE tunnel doesn't come up sucessfully and then PPTP closes the connection.
Have there been some major changes to the IOS featureset which is causing this problem? None of the configurations for any devices on the network have been changed.