Dear GCB,
I can reproduce this issue, you need change
GalleryBrowser1.GalleryClient = "~/U_CuteSoft_Client/Gallery/";
to
GalleryBrowser1.GalleryClient = "U_CuteSoft_Client/Gallery/";
After done, please try it again. I tried it on my end, when change this, it will work.
Thank you for your business