I have a rather curious issue with some workflow tasks.
My (state machine) workflow creates a handful of tasks while running. Users interact with the tasks to move the workflow between its states. Links to the tasks are sent by email and users go to the SharePoint (2010) site by clicking on those links.
From time to time though (absolutely random it seems, because I wasn't able to find a pattern) the user gets an error page and in the logs there is always this:
System.ArgumentException: Item does not exist. It may have been deleted by another user
The task is there, as a farm administrator I can access the task. But the user can't. It seems to be a permission issue but all security settings are OK and for a similar task on another workflow the user has no issue. It basically works most of the times and sometimes it just fails.
What could be the issue? What do I look for?