Maybe the .properties files have backslash escaping, so "Documents\spring-85.0" becomes "Documentspring-85.0" when read, because "\s" can't be decoded?
(Might be what you are implying.)
Nope, if I go directly to the folder using the browse button and select my spring folder, it does not add a trailing slash, and fails when saving.
Also, the settings dialogue does not ask for the absolute path of unitsync.dll it asks for unitsyncs path. Since this is immediatley below 'spring path' one assume it is the folder unitsync is in that is wanted, not the full path to unitsync itself complete with filename.
This is a cross platform bug in cheeselobby. I suggest changing the wording to make it clearer, and adding safeguards and checks. Also when loading fails, do not dump the user and crash, instead catch the failure and open up the settings dialogue shown on first run.
Also the window with the settings first shown on first run is not a normal window, as such it does not appear in the task bar, making it impossible to select without alt+Tab or minimising every other window if it goes behind another window.
edit: Upon reading the above posts, I tested out this revelation, and proceeded, only to be told "Can't find dependant Libraries". Note that the unitsync in question is from the spring portable download. I've dumped it in a folder and picked it using cheeselobby. No modifications have been made to the spring folder beyond unzipping it into that directory.