Another newbie question

I am now into a month with my 99 323i.I have performed many maint. items that were ignored by the p/o.I took a 300 mile trip yesterday,and the car is a joy to drive.Everything is great...except :hmm: After doing the rear brakes,the red ''BRAKE'' light comes in the dash.The pad warning light has never been on.Is the red light for low fluid(it is full) or the e-brake? I have good brakes,but the pedal feels a bit soft.I will go ahead and bleed the system.Could air in the system cause this light.I learned when the light is on,my cruise control is inop.Must be a safety issue.When the light is off it works normally.Thanks for any feedback.