After completing my MBA and on the strength of a number of years of public sector experience I landed my first consulting role as a "Senior Consultant" with a small yet expanding performance management consultancy. After six months, I have realised that this job is not suitable for me as I am not adding value to my skillsets. I want to move on! Now my concern is that looking for another consulting role only after six months .... what impression is this going to give to the perspective employers? Is it bad? Please help me - Thanks.

I don't think this is a big issue. You say that you have a number of years of experience so as long as you weren't moving every six months through that time I can't imagine anyone assuming you were having problems. You'll always get asked about why you're leaving your current post - no matter how long you've been in it. Explain it as you have here - it seems like a rational decision process that most people will understand.