Error: Unable to load "ICUWrapper.dll" or one of its dependancies

I'm working on an MS Word Add-in that accesses SDL File-based TM. Everything is fine when the add-in is started inside VS 2017 in debugging mode, but the error appears everytime when the add-in is started in release mode or outside VS 2017 environment.
Does anyone have any idea what is the cause behind? and offer a solution.