Hi Johan,

We have an article in our Knowledge Base system about this error message:

http://kb.sdl.com/#tab:homeTab:crumb:7:artId:8448

Please take a look at it and follow the proposed solutions.

Also I noticed in your online account that upgrade for the Studio 2011 to 2015 has not been processed.
To process your upgrade- please log in to your SDL account- LICENSES

Once logged in and on the licenses section- you will see a Gold coloured banner at the top of the page-

Simply click into this banner (upgrades available) to process the upgrade.

Kind regards,

SDL_Roman

Hello Johan,

Try this one: 

It may not seem appropriate as it was written prior to Studio 2015 but I believe the resolution should be what you need.  If you do have a problem and still cannot resolve this then please contact support.  

Go to the Knowledgebase.  Then go to the tab called Solution Finder and now go here;

Download & Installation Problems
- I use SDL Trados Studio and/or SDL MultiTerm 2011, 2014 or 2015
-- I receive an error message during installation
--- I have disabled UAC during installation / I do not have Win Vista 7/8
---- None of the error messages match my issue / I tried the suggested resolution....

So if you have tried everything suggested, when you get to this point you'll be presented with a form to contact support. Complete all the fields in the form making sure your email address is entered correctly or nobody will be able to get back in touch with you.

Also use the Chrome browser to log the case if you have it; you'll get more success in completing the form.

I hope this helps.