All questions related to installations, configurations and maintenance of Advanced Host Monitor (including additional tools such as RMA for Windows, RMA Manager, Web Servie, RCC).
Theoretically it could happen when new Web Service connects to old version of HostMonitor.
May be you have several versions installed? What version do you see on the top of the web page?
Thank you for the files. I was able to reproduce error and found mistake. It will be fixed in next version (I hope Beta version will be available next week)