Gnuradio companion block selection window missing

I just installed Gnuradio and UHD yesterday and have been playing with
Gnuradio Companion. All was going well until a little while ago when I
started it up the block selection window was gone. How do I get it back?
I am running version 3.6.3 under Ubuntu 12.04.1.

Thank you.

Problem solved.

Can you please post the solution for this problem. Even for me the block selection window is missing.