[Solved] Plugins: enabling plugin: " addon generates a fatal error "

I put the complete root from a subdomain to the main domain and now i can not enable anymore plugins; it says: "This addon can not been enabled because it generates a fatal error" and below it "Success"
I only can enable them in the config.php
I also emptied the cache ini files
What can cause this problem?
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Problem found: in my index.php i put this code at the bottom:
that causes the problem
This works fine: