I’ve updated the relevant blogs and posted a new one at http://blogs.technet.com/b/projectsupport/archive/2013/09/13/project-server-2010-august-2013-cumulative-update-installation-latest.aspx but wanted to be sure my subscribers see this too. The core of the issue is that if SP2 needs to make DB updates (usually needed – but not if June CU was installed) then the August CU will get confused by the version number that SP2 writes into the published DB versions table and fail during the configuration wizard. See the link above for your options to avoid or recover from this.
Repeating the error here just to help the search engines:
and from the Upgrade Log: