Level Manager not opening


I am trying to access the level manager to edit properties of certain levels. When I press the button, it does not open. I have tried opening it from the search bar however it still doesn't open. I have also tried to open it via Level Display by right clicking and selecting Level Manager which failed. I seem to be able to access every other feature fine. 

The Level Manager has worked for me fine in the past until recently it suddenly stopped. I can not think of any settings changes I have done that would affect this.

Any help would be greatly appreciated.

Many thanks,