Upgrading from 1.6.11 - URL's issue

[frostschutz]

This user has been denied support.

Well, if you still have problems, do show what Google SEO says on the plugins page.

It would warn you about URL scheme conflict (depending how old your Google SEO version was before, it didn't warn you).

However you can choose to ignore this warning if you took steps to prevent a conflict in this case and ordered your RewriteRules in such a way that Thread-* is checked before * - or Thread-Subject would redirect to userprofile anyway.