Whenever you work with Store Commander, interface or CSV import, you get a Fatal Error without any detailed information.
This error comes from MailChimp Integration Module, hooked onto ActionProductUpdate:
MailChimp Integration is one of the modules interferring with Store Commander's modification process.
You will find more information as well as the solution in the related article below.
Download our themed Guides to learn how to manage your shop at lightning speed with Store Commander.