"URL No Longer Exists" when trying to load VisualForce pages

Summary

If you are getting a "URL No Longer Exists" error when trying to load Visualforce pages, you may need to check your security settings.

Environment

Not applicable.

Diagnostics Steps

Not applicable.

Cause

Clickjack Protection for Visualforce pages is enabled.

Workaround

Go to Security Controls > Session Settings > Clickjack Protection and make sure the following option is unchecked:

Resolution

Not applicable.