2.3. Cookie prefix: the same as the mediawiki Prefix (the default is the mediawiki database name + prefix (mw_))
Should perhaps be clearified:
2.3. Cookie prefix: MUST be the same as the mediawiki Cookie Prefix. The MediaWiki default is prefix (mw_) + the mediawiki database name (mw_databasename). Though it could be changed in the wikis LocalSettings.php with the string: "$wgCookiePrefix".
When I figured that out it worked as a charm.