Toni - I had an issue like this with March 9 snapshot on one of my firewalls. The tunnel would go up when I restarted isakmpd on both ends, but then would stop for no reason. I upgraded to March 17 snapshot and it seemed to be OK, but I had a nagging feeling it could have been a routing issue as well.
(I was using auth hmac-md5 enc aes group modp1536 for both main and quick.) Tom
