This issue is due to the presence of Cisco bug ID CSCsd51126.
This issue is specifically seen on Point-to-Point Protocol (PPP) dialup connections on the Intel platform with a mismatch length error message in the VPN client logs.
This is sample output from the VPN client logs:
259 12:49:16.053 05/02/2006 Sev=Warning/2 CVPND/0x83400018 Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)
260 12:49:16.654 05/02/2006 Sev=Warning/2 CVPND/0x83400018Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)
261 12:49:16.654 05/02/2006 Sev=Info/4 IKE/0x43000075Unable to acquire local IP address after 5 attempts (over 5 seconds), probably due to network socket failure.
For a workaround:
Download and install Mac OS X VPN client version 4.9(1.30) from Cisco Downloads.