Yesterday I bought Responsivizer plugin for our website www.benno-haus.de.
The site is on Joomla 1.5.26 - old, I know, but there's no way to update the site in the past and the next few mounth.

The plugin installed without any problems, easily. The plugin works correctly, there're no malfunctions I see in the backend.

But the problem is: In the case I switch "enable template switcher" to on, and the theme is "Responsivizer Default", so this template doesn't work. On my mobile (Moto E2, Android), I get a "Server 500 Error". On the device emulator theres only a grey sreen, nothing happens. On Safari with "Responsive Design" Option on, theres only a blank screen, theres no source code also - very strange ...

When I set the option "Choose template for mobile users" to the normal non-mobile theme, called 'benno', everything works fine (but thats not a mobile theme, of course). Also the device emulator works, the site on my mobile also.

What could be the reason? I'm not an IT-expert, so please be patient with me, thanks!