WebCenter Content 11.1.1.8, DIS MS Word checkout error

The users of Word often get an error when checking out a doc from WebCenter Content. Here are the steps that lead to the error:

Open Native File - get local copy in Word

Go to WebCenter Content on menu - DIS

  Select "Check Out"

A message box comes up with the heading "Oracle WebCenter Content Server" and the message says "Error opening C:\Users\username\WebCenterFiles\server.domain.com:16200\172D222D\filename.doc"

The user then must reboot the computer to again access WebCenter files. This happens randomly, sometimes not for weeks, sometimes multiple times a day. These users check out 4-10 documents a day, checking them back in on the same day.