Since Holux is offline, ezTour will not be updated with new Googgle-Maps-API. Technicialy you have to renew the Google-Maps-API in ezTour yourself. You need an own Google-API licence key too. A manual may be available soon.
This is the old (outdated) answer originaly from Holux:
Holux think this problem should be caused by Google. They would upgrade and improve their Google API version in different country of google server. Holux advised to make sure whether your ezTour software would show this error message as same as below, you just need to change the google server setting to “maps.google.com”. ezTour should be working again correctly.
Try to look at the ezTour setting “Tools -> Options”. Then you will see the “map server item”.
If ezTour didn’t work and continue to display the same error message – what should you do?
Holux still got the same issue because the Google also improved its map API version to latest version on “maps.google.com” server. Therefore the ezTour software with older API version package isn’t matching and it displays this error message.
Holux had solved this problem with newer versions of ezTour by renew the Google-Maps-API licence.
Source: holux.com, translation reworked