Hello
I want to add Google Cast integration
But it failed because ''Integration already exists, and it possible to have only one integration"
Nothing into configuration.yaml
I don’t understand
It is because you have auto discovery on and so HA must have already found the device and added it. Please check if the device is there in the integrations.
I can’t see any google devices into devices integration
can you see the google cast integration in the integration page? Integration page is under sidebar>configurations>integrations. Please share a screenshot.
Its strange. Please check if there is the domain cast: in any part of your config. Also try restarting HA
Already try it …
do a cache refresh (CTRL+F5) and see
Good idee I just try it…same issue
just check if you have any media player entities with google device name.
Not in media browser. go to developer console and in states tab check if you have any media player entities.
Ok understand now, I have checked and I see nothing …
Are you running HA in Raspberry pi? If not how r you running HA
Home assistant OS, into virtualbox (host ubuntu on NUC) with official *.vdi
Did you try rebooting the virtual machine? Its very strange this happens.
I will retry
Please take a snapshot before rebooting. If something is corupted you may have to reinstall HA
Restarted same issue 
I am all out of ideas, usually this could happen if there is something left behind in config or so. But in that case there could have been some entity or devices present. Lets wait for some other to give any advise. If no advise comes its better to make a fresh install and try.