Theme logo and background image permissions

[-=Ron=-]

I'm just starting to use version 4 on a couple installations and I'm trying to modify
some of the themes,,   the logo image, the background picker image, etc.  But
when I try to select a file to upload in the theme using the "choose a single file"
tab, it's not working.   Not for logo images, nor the background picker either.  It's
like there's a permission issue on a folder that isn't set right.  It just ignores my
request to choose a new local file.  Can someone direct me on how to fix it?  I've
been experimenting with various folders via ftp but I haven't had any success so
far. 

Thanks,
Ron