Prism tries to connect to the internet with every launch, and must succeed at least every 30 days or 20 launches (whichever comes first) to confirm the validity of the license. Once it hits those limits, it displays:

"You are currently offline. Prism must connect to the internet at least once every 30 days to validate your license. Please connect to the internet and launch Prism again."

If you are getting this message even though you computer is connected to the internet, perhaps you have a firewall that prevents Prism from communicating with the internet. Prism uses port 443, which is the same port that web browsers use when browsing securely (https:), but it is possible that your IT people configured your firewall so that web browsers (and email programs...) but not Prism can use that port. If that is the case, they will need to change the firewall settings.