PVZ GW2 Files Corrupted or Unreadable

My friend has been having this problem for a week now. Whenever he tries to open GW2, he gets an error message saying something along the lines of "Files are corrupted or unreadable." I should specify that the error message comes form his computer, not GW2, in fact, GW2 doesn't even open. He's tried reinstalling, restarting his PC, even trying some alternative solutions. I should mention he plays GW2 on Steam. Does anyone have a solution or workaround?

Edit: This is the error he sees every time he attempts to start his game.