When you looked at the Microsoft Exchange Writer, did you find that it was in a "Waiting for completion" state? If so, rebooting is one option and is also recomended by Microsoft. In this TechNet Article though, it also mentions finding the event related to the service and restarting the process or service:
open Event Viewer as described in the "Open Event Viewer and view events related to VSS" section and look for events related to the service or process that hosts the writer. If necessary, restart the service or process, and retry the operation.
If for some reason that still doesnt work then you will have to reboot.