I'm getting this error:

Exception Information:
Message: Unable to obtain upload context for '039bbdc809224349a6f1f4179d71959e'. The application may have been restarted, or your session has expired.
Source: ISNet.WebUI.WebTextEditor
Stack Trace:
System.Exception: Unable to obtain upload context for '039bbdc809224349a6f1f4179d71959e'. The application may have been restarted, or your session has expired. 
at ISNet.WebUI.WebTextEditor.WebFileUploader.GetContext(String guid) 
at ISNet.WebUI.WebTextEditor.WebFileUploaderHttpModule.?? (Object sender, EventArgs e) 
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() 
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

If I logout and login again it seems to work, why is this happening?
We are using a StateServer setup, it works normally but after a while it doesn't work.

Is there a way for me to re-create the required context so this problem doesn't happen?