Daniel,
Go ahead and try adding this controller again. You should be able to do so. If you ever come across this again just let us know and we can see what might be going on in the back end data.

This does appear to now take me to the Rainmaster web page, though not to a Web Configurator as the LandFX dialogue box suggests. I assume the Model number and details of the DX2 will likely need to be entered manually in this case?

Daniel,
That is correct. The thought was to have it take you to their landing page, but is not quite there. So in these instances, yes, simply close the webpage for now and complete the exact equipment you need to show in your design. We will get these models entered and ironed out as soon as we can. Thanks for your patience!