5.7 error after installation: "Module 'pdo_mysql' already loaded"

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Hi all,

I've just installed 5.7 and everything seemed alright (and looks awesome!), but when I open my site I get "Module 'pdo_mysql' already loaded" at the bottom of every page. This also prevents me from doing any edits. Can't find any mention of people having the same problem, so thought I'd ask her. Has anyone got any idea what's happening?

Thanks,

Alex.