Problem doing optimization. Relaxing the constraint gives no Feasible solution.

Hi, I am running an optimization using fmincon.I have inequality constraints and lower bound and upper bound .Total 9 variables. If I put the upperbound of a particular variable to 0.43 ,I get "No Feasible Solution". With the following message. ----------------------------- "Optimization stopped because the relative changes in all elements of x are less than options.TolX = 1.000000e-010, but the relative maximum constraint violation, 5.646613e-003, exceeds options.TolCon = 1.000000e-006." -----------------------------

Strangely enough,if keeping everything else constant ,I change the upper bound of that one variable to 0.42 ,I start getting results.

So ,I get results when my variable ranges between 20-42 ,but no result when it ranges between 20-43. I have changed different algorithms and it is always the same. Can somebody suggest,why this might be happening?