After months or even years of working fairly flawlessly, my Cisco AnyConnect Mobility VPN client started to quit on startup. No message is shown, it just disappears. Somewhere there is some log file, but it doesn’t give too much away. Eventually I worked out that this issue relates to having Fiddler debugging proxy installed.

I frequently use the https interception and decryption feature to see webservice traffic during web development. This involves installing a Fiddler root certificate on the local machine so that the interception is trusted by the local system.

This certificate can be seen in the certificate store, or found via Action > Find Certificates, searching for ‘fiddler’.

The important part here may be the expiration date. I say ‘may’ because I don’t gave a concrete example of what the root certificate date is when the issue with the Cisco VPN is happening, but what I do know if that this issue happens periodically over long intervals of maybe a year or more and that resetting the Fiddler certificates resolves this issue, presumably by reinstating an expired certificate with a non-expired one as shown above.

To reset the certificates go to Options > Https > Actions > Reset All Certificates.

This process takes a few minutes, will many prompts to proceed with modifying certificates. As soon as this is complete, I was once again able to start the Cisco AnyConnect VPN client and connect as normal.