Office 2011 - Folders on Mac OS X Server network share not visible during save
I had the same issue. To fix it I renamed my Library->Application Support->Microsoft->Office folder to "Office Backup", allowing the program to create a new folder upon opening. After reopening, the issue was fixed.

Be sure to copy over any template files you had created (such as an updated normal.dotm file for word) from the Backup folder to the new one once you have confirmed the issue has been fixed.