You will need to change the php.ini file to account for server settings that may prevent you from uploading larger images. You say this page will upload some of the files, but not all of them, so there is a server setting that is preventing Digital File pro from allowing the file to be uploaded. Editing the php.ini file allows you to change the server settings that are preventing the upload.
When uploading an image and resizing it, the GD Library needs to be able to use a lot of memory. Changing the memory_limit setting in the php.ini file will allow the GD library use of the memory it needs.
As for using the beta Build, there was a bug found where in some cases the uploaded files where being given strange names like:
This is fixed in the beta build. we make this available for people having this problem.