Thanks Chuck. Directories are there, chmod'ed correctly, I get a lot of these errors. Could it have something to do with the way the file is numbered, with the "underscores"? Does this just pertain to the medium images, ie, I don't notice anything wrong with the forum.
Funny, this started happening after I moved from one server to another. The original photopost (on russbo.org, which will be taken down once I get this thing ironed out), works fine.