Problems referencing files in app_code folder

I have suddenly started having problems calling functions in the app_code folder of an established site. I noticed the problem when testing and finding simple pages took 20 seconds plus to load instead of the expected 1-2. Any reference to a function in the folder adds 20 seconds to page load time. Take the call out and the page loads normally. The page does not actually throw a compilation error, but it shows up as a conection error when analysing page load at tools.pingdom.com. http://screencast.com/t/jeFfoWq2psV http://screencast.com/t/jeFfoWq2psV No code has been changed, and we use these functions all the time without any problem. Can anybody suggest why this problem might be occurring? WE are using asp.net version 4