Adding equals sign in a cell gives error in the formula result bar at bottom.

Whenever I try inserting a formula by pressing equals sign, the bottom formula result bar says 'the formula should not begin with equals sign'. It gives same error message irrespective of cell format (auto, numbers, currency etc). Please check screenshot. Just to inform, it calculates and gives correct results in both conditions when formula started with equals sign and when without equals sign. Why's it giving that message???

[Edited by Moderator]