You cannot attack in your current stance

[Dalit Ascension]

how do i fix this?

[Bracinjo]

You have to wait for the next turn, get out of that stance and attack.

[Schnitz]

change stance

[L3TUC3]

Set stance to none.

[ranger0440]

you can't attack if you are in forced march or the fortify stance, and the ambush only allows ambushes

[ATT]

Depends on what the situation of your troops is. If you are recruiting he enters muster and cannot move until ALL recruiting is complete (so if you have a turn backlog of say five turns it must be cancelled), if he has been set to a stance manually by you (ie raiding) select the army then select the button which I believe is far left and revert stance to 'normal' which will allow you to give move orders as appropriate. If none of this works it may be a glitch as I have heard reports of similar events.

Hope that helps

EDIT - The stance is I think in actuality called none not normal but if you hover over it you get the info anyway