A spate of errors haver appeared for many users of Microsoft Dynamics CRM 2013 in the past couple of days
When users try to open a lookup they get an error:
[red and white cross in a circle]
An error has occured
Try this action again. If this problem continues, check the Microsoft Dynamics CRM community ...
Google Chrome version 38
This error coincided with the release of Google Chrome 38 and appears to be the issue. Either use Internet Explorer, Firefox or go back to version 37.