> því að vitringinum Eyjólfi hefir nú yfir sést
"because the wiseman Eyjólr has overlooked something (made a mistake) now"
Do I sense a little sarcasm here? <vitringr> is dative singular, <vitringi>, with the suffixed definite article -(i)num. It's in apposition to <Eyjólfi>, also dative. The plural would be <vitringunum>, with <u> instead of <i>.