We have a similar issue:

- IE 8 works well with Visual Studio and IIS < 7

- all other Windows browsers work well with every webserver

- with IE 8 and IIS, the "collection is read-only" error shows after upload

- adding<add key="CuteWebUI.AjaxUploader.UseAspNetStream" value="True" /> to web.config solves the issue, but the progress bar is not shown anymore

 

It seems strange that only the specific combination IE + IIS7 produces that behaviour, no matter if Flash or Silverlight are used.

 

Any ideas?