TYPO3 v6 has reached its end-of-life April 18th, 2017 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

There is no further ELTS support. It is strongly recommended updating your project.

Remove temporary cache files

In typo3temp/Cache/Code/cache_core you will most likely find files named ext_localconf_*.php or ext_tables_*.php. These files must be removed as well.

Go to "Important actions" and click "Clear all cache":

The option "Clear all Cache" in the Install Tool.

This method will remove all files from the folder typo3temp/Cache/Code/cache_core/.

Additionally, after an upgrade to a new major version, you should also delete the other temporary files, which TYPO3 saves in typo3temp/. In the Install Tool go to "Clean up" to do so.