We had this error while we were debugging our VPNs to our PIX in lab tests. I did a “debug crypto isakmp” on the pix and discovered the problem, (mismatch of options). If isakmp is working properly you can try “debug crypto ipsec” to see if the problem is in stage two of the negotiations. If you want to view encrypted traffic try “debug crypto engine”. Remember not to leave it in debug mode, (uses up too many resources).