Cannot add audio to track

Hi, I am new to Storyboard Pro and I must be missing something very basic. I had audio clips on my timeline for multiple tracks and had to delete them. I need to update with new audio. But now for some reason I cannot import the new WAVs. I tried dragging the audio manually onto the timeline and I get a Circle-No icon on my cursor. I do not have my tracks locked. Can someone identify this newbie solution for me? Thanks so much!