Custom Warning Popup

I've seen a couple different example of a custom popup warning dialog box that will come up when the networked workspace cannot be found to give the user a warning that it is switching to the local workspace. I can't remember exactly where I saw this and am unable to locate any sample file. How could this be done? I currently have a CFG file with an if/then statement looking for the network version of the workspace, and then using the local version if it isn't found. Any example CFG file with this warning dialog would be helpful.


Thanks,
Ken