What size are you trying to upload? 1024x768 is Auctiva's maximum size allowed. If you try to upload a larger size, the uploader should reduce your image size to 1024x768(but not smaller). I just now uploaded a 2400x1700 pic. Auctiva reduced it to 1024x768, but the upload took forever(several minutes, the first attempt locked up!). If you upload 1024x768 or smaller, the original size will be retained and will upload MUCH faster since no extra processing takes place. I just uploaded a 800x600 pic in 2 seconds, with no reduction in image size or file size.
The process works best if you reduce your pic size on your pc first. 800x600 is an optimum size. Also reduce your file size to around 100KB (image quality='normal')for easy download by your dial-up buyers, and faster upload by you. Your pics will get reduced to a 400x300 thumbnail in your listing, with a 'supersize' link. The supersized pic will be displayed at your original size, in this case 800x600.
If you still have this problem while trying to upload at these sizes, I would file a support ticket. For me, the uploader works normally and I don't know of any setting that could be causing your problem.
PS -I have heard that uploading all your pics BEFORE adding them to your listing works best. Apparently uploading directly into the listing has given some people trouble, although it works fine for me. (Perhaps this is your problem?)