About the rankings: did the tool show rankings for those keywords before? If so, I would write SEOmoz support to help you out (or wait until tuesday to see what happens). If those keywords are recently added you'll just have to wait until the new update.
The drop in the errors in huge indeed. Do you know what kind of errors it were? Did you change a lot on the site? It's hard to give you an answer not knowing the issues.
