Why cant you print the e-ticket?

I dont know about over there but as long as you know your details [ticket number etc] it dosn't cause a problem in the uk [may be a small charge]

But I would worry about the other end the yanks have funny ideas if you do not have all the necessary paperwork for your trip

I have never needed to show an e-ticket for a scheduled flight. All that has ever been required is your passport. That includes umpteen flights FROM the US.

Have you tried printing it out from a different browser (e.g. Chrome, Firefox, Internet Explorer)? Sometimes Chrome won't let me print things but IE will.