When I updated my Lion Macbook through "Apple Update" it impacted my Cisco VPN certificate.
Prior to the installation my security cert. was valid but after installation the cert. issuer became invalid. I have not changed anything nor is the time on my laptop the issue. The certificate is still valid prior to the update and I have gone through a fact check with serveral installations, so I am very confident it relates to something within the update.
MacBook Air (11-INCH, MID 2011), Mac OS X (10.7.4)
I found a fix for this, you have to update the IP Security field within the related CERT's in KEYCHAIN Access. Only change this field to "ALWAYS TRUST" and you should be able to use these CERT's for access to VPN.