Ok, so basically, I added the upload_files capability for contributors using a plugin like "Capability Manager". This adds the "Upload/Insert" icons for contributors just above the post edit box when they edit posts. It works flawlessly without Role Scoper.
When you add Role Scoper, the Upload/Insert icons seems to work at first when creating a new post as a contributor... But if you save a draft and return to it later (as the same contributor), then the Upload/Insert icons will be gone!!!
Deactivating Role Scoper solves the problem temporarily as I haven't really used Role Scoper yet, but I intend to use it soon.
Can you look into this bug? I'm not familiar on how to use Role Scoper yet, so perhaps there are setting I can change in Role Scoper to fix this, or perhaps it is actually a bug.
Thanks! And great plugin!