That thin layer of yeast is a good sign.
To get rid of it, simply cool the bottle down in the fridge, and then open it up, and slowly pour the beer into a glass, leaving about a tablespoon of beer in the bottle, with the yeast sludge. Drink the beer, and rinse the bottle out!!
The sludge is just yeast that has dropped out of suspension, presumably after finishing all the sugar in the beer, carbonating it etc. The yeast has the additional advantage of being an oxygen scavenger, which is to say your beer will stay fresh tasting for a good long while because of it.