I was able to FILE-->EXPORT-->AUDIO (Master bus only) to .mp3 before... but the current project I am working on, when I do the same steps.. It takes really long time and gets hung. 20 tracks (all frozen) going to master bus. Tried .wav, same thing. Any suggestion? First time, on this project, (when it didn't get hung) it created a 700mb mp3 file, I deleted it right away thinking something was wrong, didn't check if it played the song. 
Thanks in advance.

It could be an event or multiple events like an automation nodes or midi data far to the right on the time line. Clean up the project and/or specify a time range to export.

Will do that when I go home... 
How do you specify time range when exporting to mp3 or wav?

After selecting the tracks to export either click-drag across the timeline, use Select by Time or a combination of Select From & Thru from the Edit menu or add markers an select between markers.