There is a warning in the tutorial rendered by HarryH, that once you open the editor you should not close it without importing a mission file or it will cause an error to WOFF. Not sure if this is still the case because his comments were related to WOFF3 and not WOFF UE. Hopefully someone will update the tutorial for WOFF_UE.
Robert, I've opened the ME numerous times without then importing a mission file and have had no issues at all. Also, here is another screenie showing how the ME can be pinned to the task bar for a one-click launch after hitting ALT-TAB(right click on image and open in new window to view it full size)