Hi and welcome Stefan!
There could be a couple of different things causing this but following the ThermIQ installation guide step by step is proven to work. Some small deviations like not rebooting when stated could cause hickups like this.
Anyway, try these steps:
* Check that you have the latest release of Raspbian “Jessie” downloaded from raspberrypi.org(full or light version shouldn’t matter)
* Flip down the output field of the install window, what messages do you see when you choose “Update”. Anything that can be fixed?
* Try a reboot
If nothing else works then restart from beginning with a clean install then follow installation guide to the word.
Good luck!
/Anders