Did this just start happening? This might sound like a useless suggestion. But try restarting your computer.
Is it a CS5 problem or a LR problem or just the combination?
Try opening the same image directly in CS5.
Try defining another program as an external editor and see what happens when you use Edit In that program.
Try turning off (or on) Use Graphics Processor in PS / Edit / Prefs / Performance.
Make sure your PS CS5 is up to date and or do a reinstall of PS CS 5 over the top of the current install.
Thanks to all who responded. I have done a full reinstall now and things have improved. The main issue now is the total lack of ability to update my cs5 programs as Adobe has no interest anymore, forcing us all to invest more money in cs6 cloud!
PS CS5 is now 6 years old, came out 04/2010 and CS5.1 in 05/2011. Adobe came out with CS6 05/2012. It is now 04/2016. Do you know of any software company that supplies updates for 4-5-6 year old software especially after they have released at least one newer version?
You had ample time to upgrade to CS6 3-4 years ago. But even CS6 is no longer receiving updates. Even if you have a CC account.