Hello and welcome Lwee
This error is a normal behavior ... it is to prevent potential errors during WinReducer use due to Microsoft folder path length limitation ... to solve this error you just need to move your EX-100 folder to a different location in your HDD/SSD.
For example : "C:\WinReducerEX100" or "C:\Program Files\WinReducerEX100" or better "D:\WinReducerEX100" (if you have a second partition in your HDD/SSD)
Please let us know how it works.
I wish you to have a great day !