Hi Jakob,
any progress in this matter? I am facing the same, actually, even though on different software versions:
Win7 32-bit, SAP GUI 7.30, patch level 6. I have JRE 6,7 and 8 installed (I have enabled them one by one in Control panel without any luck). The problem is the same, see attached (the curious thing is that it even asks for having SAP GUI 7.20 installed - and I am installing 7.30). Still, I think that JRE detection is the problem.
Thank you, Michal