A few days ago I accepted a friendly match, and a re-match when I switched for scoiatel deck gwent crashed and I've been tryin' different things lookin' to have the play menu working again, something about UnityPlayer.dll error.
It is very common to get an error of Unityplayer.dll. The fix is so simple. The URL: https://dlldownloads.com/unityplayer-dll/ will fix your current error. But also, consider updating your drivers, old drivers might be the culprit for your error.