Hi Carrissa,
It sounds like there is either something about the images you are trying to upload that the Auctiva Uploader does not agree with or that your system does not have enough memory available to support the resizing that the uploader does using your system resources. If you continue to experience this problem, I recommend contacting our customer support team using the form on the following page of our site: http://www.auctiva.com/help/requesthelp.aspx
In the interim, you could potentially try using the HTML Uploader, which can be found by mousing over the "Images" tab within your account, selecting the "Upload" option, and then clicking the "Basic HTML Uploader" link on the ensuing page.
If you would like to adjust your account so the HTML Uploader is used on the listing creation page by default, you can do so by mousing over the "My Account" tab within your account, selecting "Acct Preferences" under "Settings", checking the box next to "Use HTML Uploader on One Page Lister" and then clicking the "Update Account Preferences" button below.
-Mike