What browser is this occuring in? Does the problem go away if you wait for a few seconds after clicking the cancel button before clicking your other buttons? If so, perhaps the upload hasn't actually been stopped yet and the browser is ignoring clicks on other buttons until it has stopped. Not sure, just a theory...
Are you using LinkButtons or regular Buttons? NeatUpload 1.0.12 doesn't support LinkButtons, but the latest development snapshot (NeatUpload-trunk.95.zip) does. If you just want links that take the user to other pages (but not actually submit the form), in NeatUpload-1.0.12 you should be able to use regular <asp:HyperLink> elements or plain HTML <a> elements. The live demo uses the latter for the link to the NeatUpload home page.
If you decide to use LinkButtons with the latest development snapshot, you will want to list them as NonUploadButtons if you don't want the file uploaded when they are clicked. See the manual that accompanies the dev snapshot for details on non-upload buttons.
If you aren't using LinkButtons, can you send me (dean at brettle dot com) the aspx/aspx.cs files you are using so I can try to reproduce?
Got the files. FYI, my mail goes through gmail which refuses zip files containing exes.
I'm not going to be able to test the files personally for a little while because I'm having problems with my Mono installation at the moment. However, I did look over them and I think I know what the problem is. When you click the redirect button, the browser is submitting the form including the large file. The file takes a long time to upload but no progress bar is displayed/started because you didn't call progressBar.AddTrigger(Test_Redirect). So, it looks like the button isn't working, but in fact you will get redirected if you wait long enough for the file to upload.
To test this theory, time how long it takes to upload the file without cancelling, then try to reproduce the problem but wait the same amount of time to see if you get redirected. Alternatively, after cancelling the upload, clear the filename before clicking the redirect button.
Are you sure you can't use a regular link? If the session id is maintained with a cookie, I think the session will be maintained as long as you are redirecting within the same domain. If the session id is maintained in the URL (aka cookie-less session), using a relative URL should still work.
and then call it from your redirect button like this:
If that doesn't do the trick, the best I can recommend is using the development snapshot. FWIW, switching should be relatively painless, will result in cleaner code, and will get you other nice features like AJAX-style refresh-less updating of the progress bar.
PS. Thanks for mentioning NeatUpload on your blog and home page!