Bugzilla: error which isn't error

The local XML file './data/bugzilla-update.xml' cannot be created. Please make sure the web server can write in this directory and that you can access the web. If you are behind a proxy, set the proxy_url parameter correctly.

If you got this error and you are sure that the user who started the web-server can create files in data/ folder, then just check if Bugzilla's update server is up. For doing this go here and check address http://updates.bugzilla.org. If you get 500 read timeout or some other error, then obviously it's not your fault and you simply need to wait several hours, otherwise keep googling.