Camera will not take picture at times

[vsbill17]

I am a novice Rebel T4i user.  I have been shooting in Manual mode but at times I do switch to either Shutter or Aperture Priority.  At times my camera will not take the picture when I press the shutter and the aperture number will flash.  There is also a red dot that flashes on the lower right when I look in the view finder.  Is this from the settings I am using are either over or under exposed?

Thanks,

Bill

[cicopo]

I don't have any Rebel bodies but I'm pretty sure that red light means the AF hasn't locked on anything. When the AF is satisfied it has done it's job the light is green. Also the flashing aperture number implies NOT ENOUGH LIGHT, can't open any wider. In other words you need to either raise your ISO or lower your shutter speed because the lens needs to open wider than it can at your chosen settings. 

[vsbill17]

Thank you.  I will try with the AF off.  Last night was my first encounter with this problem when we were out shooting night pics.

Thank you again,

Bill