Unable to upload non-graphic files with MultiUpload when useFlashIfAvailable="true". Setting this to false, allows uploading any file type. Setting FlashFilterExtensions does not work either. Browse window opens, allows selecting of non-graphic file types, but does not display in page (and therefore does not upload). Tested in Firefox 3.0.10 and IE 6 SP3. Apparently, it does work correctly in IE7.
I can't reproduce the problem. I just used Firefox 3.0.10 and Flash Player 10.0.22.87 to upload some WMA music files to the second MultiFile control on the NeatUpload-version/dotnet/app/Brettle.Web.NeatUpload/Demo.aspx page. That control has useFlashIfAvailable="true", and it worked fine. What version of NeatUpload and Flash Player are you using? What is the name of the file you are trying to upload? Can you upload to the Demo.aspx page in your environment?