I noticed that building OpenVPN with --disable-server fails. Turns out to be a problem with the management server and the commands it allows. I've attached a simple patch which fixes it, not sure if it's "right" or not...
diff -Naur openvpn-2.1_rc18/manage.c openvpn-2.1_rc18-dynamic/manage.c --- openvpn-2.1_rc18/manage.c 2009-05-30 21:34:12 +0000 +++ openvpn-2.1_rc18-dynamic/manage.c 2009-07-11 10:26:03 +0000 @@ -995,10 +995,12 @@ { msg (M_CLIENT, "SUCCESS: pid=%d", openvpn_getpid ()); } +#ifdef MANAGEMENT_DEF_AUTH else if (streq (p[0], "nclients")) { man_client_n_clients (man); } +#endif else if (streq (p[0], "signal")) { if (man_need (man, p, 1, 0))