I have recently set up a new adgroup containing an individual keyword that according to MSN's own research tool gets in the order of 108,000 searches a month which should be an average of around 3,600 a day (I appreciate things can fluctuate daily).

The first day of the campaign I enjoyed loads of impressions, ctr and profitable conversions (average position of 2.25) but since then impressions have dropped off to 150-200 a day! resulting in next to no traffic at all? could somebody explain this to me?