Hello Roopangee,
regards the server error:
Could you please check if the document is published?
Does the Preview mode in CMSDesk work correctly?
Are other templates working alright?
Regards the FCKEditor:
You should use only the CMSEditableRegion control (
http://devnet.kentico.com/docs/controls/cmseditableregion.htm). No other controls are necessary. It includes the FCKEditor toolbar inside - you need not to use two controls.
Best regards,
Helena Grulichova