I have a few 10.6.8 users with the last official Cisco VPNClient.app, 4.90.280, who continuously received the "error 51" on launch despite not being booted into 64-bit.
sudo kextload /System/Library/Extensions/CiscoVPN.kext and/or
SystemStarter restart CiscoVPN fixes the problem, but only temporarily.
Yesterday I found a forum post that suggested changing the order of the JREs in the Java Preferences app:
If you insist on using that g-dawful Cisco client applet then try this: Open the Java Preferences application, click the General tab and look to see whether you have both 32-bit and 64-bit versions of Java installed. If so, click and drag to place the 32-bit version above the 64-bit version... Then click the Network tab and click the button to delete cache files.
So far this seems to have fixed error 51; my question is, does anyone know a way to change the JRE order via command line, so that the 32-bit JRE is the default?