Did you create a new gallery after you created the two folders? You'll need to.
Can you look with ftp to see if the new folders are getting created when you make a new gallery? They will be svmanager/g2/images and svmanager/g2/thumbs (assuming your new gallery folder is g2). What permissions are the g2, g3 (or whatever) folders getting?
You could try upping the permissions on all folders to 0777 but I think if the permissions were wrong you would be getting error messages all over the place, not just this one. Would be worth checking that the permissions of all the folders including the svmanager folder are 0755 but maybe you've already done that.
Reason I asked what version you were on is that a new version has been released very recently and it might make a difference but it's good to check-out your existing installation before you change anything else.
SimpleViewer Support Team.