Strangely enough I am having the exact same problem. OPENBSD 5.4, etc. Phase I works once I tweaked my isakmp settings to match IOS7's capabilities (no modp2048 mainly), but I get the same messages Matt does on phase II.
I have a npppd PPTP tunnel to the same server that works fine. It is just L2TP/IPSEC that has the issues. Mike
