Try resetting the emulator .exe path. I got that error with Citra and to be honest I do not remember exactly what I did, but I remember reselecting the path was one of the last things I did and the error went away. Again, not saying that was the fix, but worth a try.
Edited:
Just got the error with PS3. Changed the exe path to a completely different emulator and saved it and exited the Manage Emulators screen. Then went back in a edited it back to the correct exe path and no error. If that did not work try closing LB after you make the first change. Then reopen LB and edit it back to the correct .exe path.