This is a WCM 6 exception. It happens when the author tries to save new content after the "Expiry date and Time field properties" were changed in the "Default Content Settings" in the Authoring Template.
Solution:IBM suggested the installation of 220.127.116.11-WCM-PK57002.zip
For more details, see: http://www-1.ibm.com/support/docview.wss?uid=swg1PK57002
IBM recommends 17 additional fixes that need to be applied before the expiry date issues is corrected:
PK54658, PK53869, PK53463, PK53575, PK53183, PK52815, PK52906, PK52802, PK53868, PK55366, PK55082, PK52688, PK51512, PK53899, PK52903, PK51892, PK55773, WCM 18.104.22.168, PK57002