Creating a Photo Gallery Extension on the Publish Form - Error When File Uploads

I am creating my own extension on the publish form. Everything is working, even the fileupload, e.g. it gets uploaded to the desired folder, but instead of continuing on to the, yeah you published a new weblog item, I get an error.

The following errors were encountered * We were unable to upload your file. Make sure your upload directory has the correct permissions set. Return to Previous Page

I cannot find any documentation on how to implement a file upload correctly on EE. I have tried to use the file_upload module as an example, but it is using the core.upload module, which would allow me to do some of the processing that I need to do. I have also looked at the extension ext.mh_file_ext.php, but that too isn’t doing what I want to do.

The gallery that I am trying to create allows for an unlimited # of images to be uploaded to a weblog entry. It is a tab like the tabs module. They are not stored as weblog custom fields, but in their own table. Again, I suppose that EE is expecting some kind of ‘response’ or error or success message, that I am not providing…

Please help.