I had a problem with Cubase 6.5 (distorted Mystic patches), uninstalled Cubase 6.5
Re-installed Cubase 6.0… loaded the program and BAMM ! “No valid Licence” updated to 6.0.5 … THE SAME STORY … “No Valid Licence”. what the h3ll is going on ?!? 
I have a track (an “almost” finished one) with midi (2 mystic presets) that plays distorted.
AND I CAN’T GO BACK ! 
Great
Downloaded and installed the latest e-licenser sofware…?
No. but why would I ? it won’t make a difference. cubase 6.5 loads. all other version don’t.
Besides, the “latest” version in the one that came with 6.5.
Well, then don´t…
The latest e-license software should be installed after re-installing C 6.0. Which, depending on how exactly you installed, uses an older e-license database than C 6.5
I can recommend the same: last version of eLCC can help you.
This happened to me. I had a CB4 license show up as “missing” on my older laptop until I updated e-licensor. It then opened fine as normal.