Is your ImagesUpld directory really inside your UBB directory? I have my image and log directories outside of my UBB install.
I have my Control panel input boxes looking like this:
http://www.ssharold.com/ubbuploads for images in this directory: /home/cPanelusername/public_html/ubbuploads
And I have the logs sitting in the home area that isn't viewable to the public:
/home/cPanelusername/ubblogs