My Cask beer is flat and tastes off?
Your beer might be too cold. Check cellar temperature it should be around 52-53 degrees Fahrenheit 13 degrees centigrade.
How long has your beer been on service, it might be past its best?
Was your cask vented properly?
My Cask beer tastes of vinegar and has off tastes?
Your beer has been on service too long and has gone off. Probably infected