When we start SharePoint Designer workflow, which updates an item in the list, from code on custom web part page (with custom webpart added on it), we got following error:
System.Workflow.Runtime.Hosting.PersistenceException: Updates are not currently allowed for GET requests...
SPWeb.AllowUnsafeUpdates=true; so this is not a problem. When we start this workflow manually, or from event receiver for example, everything works fine. Error occurs only when we start it from custom web part page. When we start a workflow which doesn't update an item everything works, too. Also, if we use Pause For Duration (5 minutes) action in workflow before update, it works! Do you have any idea?