PS Could this have hapened because of the fact that the Senate loves me more than them???
No, this would have happened even if the senate favoured them above you.

When a faction, even allied, thinks you tried to scr*w them ( think diplomatic deal gone wrong - or exeptionally well ) the Ai gives you this message.

Basicly meaning : don't try this again ( ... it might just end our Alliance )

Anyway, getting these messages ins't that big a deal, since you have no way , other than this message, to see if that faction now thinks less of you or that nothing has changed between the both of you.