There is a confilct between ajax search pro and Event Espresso. I did this by systematically going through and deactivating/reactivating plugins until i found the issue between ajax search pro and event espresso.
The problem occurs when you seach for a product and go to the search results page, then hit the back button, then hit the forward button. After trying to go forward i get an ERR_CACHE_MISS. I can reload the page and it works, but when going back then forward it goes to error page.
I have tried disabling the ajax options and tried with ajax active for search pages.