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Error: "Forbidden" or "Error opening URL"
For a folder, the error message is of the "403 Forbidden" type, for a folder it is "failed to open stream: Permission denied".
In this case you should check that the permissions for your files/folders are correct, i.e. 644 for a file and 755 for a folder. You can only do this for the file that you are trying to view (or the path for the file that you are trying to view) and not for your entire hosting space.
However there are many other cases where you may get a "403 forbidden" message and this may be for various reasons (php scripts, perl, mod_security, .htaccess, ...).
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