Thanks for your feedback,
Units of activity type were different while confirmation posting was done, is that the reason for the error..?? I have attached a screenshot of basic data 1 screen; I guess the units (KWH, HR) for which error is coming in co13 is not related to the unit of measure of my FG material as it is maintained in BAG. I have option here to link up other units with BAG, how could I relate here between KWH & HR. Please explain....
Activity unit for activity type in w/c
At Present In Work center During Confirmation Posting in 07.07.2015
Labor HR Labor HR
Machine HR Machine KWH
Power KWH Power BAG 
Prod. over MT Prod. over MT