The VPN specific update didn't fix my problem nor did the Server 3.0.2 update released 6th January.
I have my router configured to forward VPN requests via UDP on port 1701 and requests via TCP on port 1723 to my server. To be thorough, I've also tried port 1701 on TCP as well.
I have my VPN in server 3.0.2 set to accept both L2TP & PPTP connections.
I have deleted and re-created the VPN service on my iPhone 5S verifying the username and secret key are identical to the server settings.
Strangely on the iPhone, it seems the only way to switch between L2TP or PPTP, is to make a change in the VPN screen for that specific tab and then hit the save button, rather un-authordox I think!
If I make a change to the PPTP page in the VPN settings screen on the iPhone (which seems to be the way you switch to using PPTP), wwhen I try to connect, I get the following error in the Server VPN log:
Tue Jan 7 09:26:54 2014 : DSAccessControl plugin: User 'vpnaccess' authorized for access
Tue Jan 7 09:26:54 2014 : sent [CCP ConfReq id=0x1 <mppe +H -M +S -L -D -C>]
Tue Jan 7 09:26:54 2014 : rcvd [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns3 0.0.0.0>]
Tue Jan 7 09:26:54 2014 : sent [IPCP TermAck id=0x1]
Tue Jan 7 09:26:54 2014 : rcvd [LCP ProtRej id=0x2 80 fd 01 01 00 0a 12 06 01 00 00 40]
Tue Jan 7 09:26:54 2014 : MPPE required but peer negotiation failed
Tue Jan 7 09:26:54 2014 : sent [LCP TermReq id=0x2 "MPPE required but peer negotiation failed"]
Tue Jan 7 09:26:54 2014 : Connection terminated.
If I make a change in the L2TP page in the VPN settings screen on the iPhone (which seems to be the way you switch to using L2TP instead), I don't get any connection detail at all show up in the Server VPN log, as-if the L2TP requests are not making it to the server!?