After our organization updated to the latest version of CiviCRM, our users started receiving the following error after registering for events on our website:

Sorry but we are not able to provide this at the moment.

Could not find valid value for id

Return to home page.

The user is properly registered on our system and receives a confirmation email. It seems to be a problem with the thank you screen. The configuration of the thank you screen is the same as before.

Ideas?