Adding a Marketing list to PowerMailChimp Blast

Hi there,

I'm creating a PowerMailChimp Blast and when I click on the + sign to add a marketing list, nothing is happening.  I'm expecting a pop up window to appear with the details to select a marketing list.  The only thing I see happen on screen is that on the bottom left a small note that says 'javascript;' appears briefly and then disappears.  

So far I've checked that my pop ups are not blocked (I also don't have an issue with other pop ups), and I've confirmed that there are marketing lists available to choose.  I also re-imported the latest release into the solution in sandbox (not yet done production).  Would anyone have any ideas?