The Install Tool is locked
To enable the Install Tool, the file ENABLE_INSTALL_TOOL must be created.
In the typo3conf/ folder, create a file named ENABLE_INSTALL_TOOL. The file name is
case sensitive, but the file itself can simply be an empty file.
Alternatively, in the Backend, go to User tools > User settings
and let TYPO3 create this file for you. When you're finished, you can also visit
User tools > User settings and delete the file from there.
For security reasons, it is highly recommended that you either rename or delete the file after the operation is finished.
As an additional security measure, if the file is older than one hour, TYPO3 will automatically delete it. The file must be writable by the web server user.