Hi,
I thought I had the same problem with my SGS3. Connecting and then opening with file manager resulted in the same message in a red bar beneath the window. Recently I found out that kio-mtp is too fast for my SGS3. If I wait just a little while and then klick the reload icon, the phone is connected and I have full access. Did you try to reload? Perhaps it solves your problem. I use konqueror, but I think the behaviour should be the same.
Download photos with gwenview doesn't work here either, but with digikam it does.
Regards dsat