We have a really odd problem here - After years of running fine we're suddenly running in the exception:

9Rays.Net FlyTreeView for ASP.NET 2.0 evaluation period has expired

These exceptions are appearing in some apps but not all. Sometimes an app that was working yesterday starts throwing the error today when an apparantly identical app on the same machine is running fine. Sometimes copying the NineRays.WebControls.FlyTreeView.dll and xml from a working app fixes the problem and sometimes not. I cannot see what's changed. Any ideas?