It sounds like you have a development snapshot of Brettle.Web.NeatUpload.dll installed in your bin folder but your NeatUpload subfolder was copied from NeatUpload-1.2 release. Try copying the Brettle.Web.NeatUpload.dll from the NeatUpload-1.2.30/bin folder into your app's bin folder.
I am having the same problem too - Microsoft JScript runtime error: 'NeatUploadPB' is undefined
my code in aspx page copied from your demo under "NeatUpload-1.3.18\dotnet\app\Brettle.Web.NeatUpload" with a control name - ProgressBar1 modified:
I am using 1.3.18 version.