If you're trying to install extra content or update and you get an error message saying RapidStudio isn't installed, this means that RapidStudio's registry entry is damaged or missing.
This could happen because of a failed update or an install that didn't complete properly or a registry cleaner that thought it was safe to remove the entry.
The fix is quite easy.
Download this registry update
Right-click to edit it before installing it.
When you edit it, make sure the "AppFolder"="C:\\RapidStudio" entry correctly points to your rapidstudio software folder. all "\" in the path need to be double, as in the example.
When you're done editing it, save the cahnges and then install (double click) it.
You should then be able to install software updates and new themes and templates.