Error 6 appears to be a very generic term in that people have resolved it in many different ways.
These have included
Reformat the hard drive. I hope this isn't necessary but, depending on your situation, it may be a "quick" fix. Source
An issue with the license (not found/recognized/valid/expired etc). You could try and reset it.
As per your post, resetting the preferences some times helps
Make sure you're running as an administrator. You can even right click and "run as administrator" to see if the fault is with permissions.
A reinstall may be required with your antivirus switched off.
You may have corrupted hard drive, run scandisc /f from command prompt.
Also, make sure you have the latest update and all patches etc are installed.