System.Web.HttpUnhandledException

On our SharePoint site there is a Wiki Library, when someone is editing a page and the select link from SharePoint; then browse on the left to the site and then to documents, then folders. Then thy click a folder on the right it they receive something went wrong an unexpected error has occurred.  Looked up the correlation id and got this:

Area     : SharePoint Foundation
Category : General
Level    : High
EventID  : ajlz0
Message  : Getting Error Message for Exception
           System.Web.HttpUnhandledException (0x80004005): Exception of type
           'System.Web.HttpUnhandledException' was thrown. --->
           System.NullReferenceException: Object reference not set to an
           instance of an object.     at
           Microsoft.SharePoint.WebControls.DateTimeField.Validate(Boolean
           validateMemberControl)     at
           Microsoft.SharePoint.WebControls.DateTimeField.Validate()     at
           System.Web.UI.Page.Validate()     at
           System.Web.UI.Page.ProcessRequestMain(Boolean
           includeStagesBeforeAsyncPoint, Boolean
           includeStagesAfterAsyncPoint)     at
           System.Web.UI.Page.HandleError(Exception e)     at
           System.Web.UI.Page.ProcessRequestMain(Boolean
           includeStagesBeforeAsyncPoint, Boolean
           includeStagesAfterAsyncPoint)     at
           System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAfterAsyncPoint)

Ideas?