I found a few suggestions that the finder webdav client sends files with chunked transfer-encoding, which I don't believe AOLServer decodes for entity bodies. If so, this is probably not easily fixable from the dav code, since by the time the dav code gets control the request has already been read (or more likely, not read in this case).
Are you seeing any error messages in your server log? Or the request log might show some kind of error status on the webdav PUT request.
