I am having the exact same problem. I have an Arduino Uno board that was uploading and running programs the day before yesterday. Then yesterday it stopped allowing me to upload. The web-based IDE says verifying, then says uploading, then just continues to say "busy"but then there is no further activity. I can no longer run new sketches.
I have tried two known good Arduino Uno boards, three different computers, and three different USB cables. But nothing I have done makes it work.
Please help as soon as possible!