NeatUpload is no longer used in mojoPortal. If you are using the latest version you should make sure you have no more references to NeatUpload in the Web.config file. It has been removed from the Web.config file that ships with mojoPortal. When you upgrade you should use the latest Web.config file and re-apply any customizations such as the machine key from your old one.
You can also remove the Brettle.Web.NeatUpload.dll from the /bin folder
Hope that helps,