You've a duplicate plugin installed. That column index was made unique in RC2, but we've since reverted that for next release. Quickfix as follows.
IN: administrator/components/com_comprofiler/database/database.cbcore.xml
ON: Lines 755 - 760
FROM:
Code:
<index name="element" type="unique">
<column name="element" />
</index>
<index name="folder" type="unique">
<column name="folder" />
</index>
TO:
Code:
<index name="element">
<column name="element" />
</index>
<index name="folder">
<column name="folder" />
</index>
Once done run the Check Community Builder Database tool and it'll ask if you want to fix it.
Note there's also a unique index for tabs that was also reverted, which you can fix with the below.
www.joomlapolis.com/forum/6-news-and-publicity/226269-next-generation-community-builder-20-rc2-released?start=24#248378
krileon
