There are a number of known BSOD bugs:
Sev Bug ID & Title Found-in Version Fixed-in Version Status 2 CSCdu43043 client causes win98 2nd ed. to crash with token ring adapter 3.0(1) 3.0(3.B), 3.5(0)REL Resolved 2 CSCdy69001 Windows 2000 and XP blue screens with 3.6 version of client 3.6(1) 3.6(3)REL, 3.7(1)REL, 3.7(2)REL, 4.0(0)REL Resolved
2 CSCdx89079 Blue Screen passing http data when ZoneAlarm is installed 3.6(64) 3.5(3)REL, 3.6(0)REL Verified 2 CSCdy62397 Blue Screen after running an overnight dial/hang test with Sygate 4.0(5) Verified 2 CSCef45028 Win XP blue screen with sygate personal firewall 4.0(2), 4.0(4), 4.0(5) 4.6(2.11) Verified 3 CSCdv81538 Blue Screen on XP when Reinstall Client with BlackIce on PC 3.5(82) 3.5(3)REL, 3.6(0)REL Verified 3 CSCdz32947 Enabling Cisco Stateful Firewall causes one machine to blue screen 3.6 3.6(3)A, 4.0(0)REL Resolved 3 CSCea29015 CVPNDrv.sys can cause windows IO Manager pool corruption 3.6 3.6(3)C, 4.0(0)REL Resolved 3 CSCea35561 802.1x EAP-TLS and CVPN Client crash the PC 3.6(3) 4.0(3)REL, 4.0(3)B Resolved 3 CSCsa57346 VPN Client driver fails to pass MS HCT 4.6(1) Verified
Upgrade to the latest Cisco VPN client.
If problem persists, then open a case with the Cisco TAC.