Hii Jino ,
This usually happens when you have certain report filters or Input Controls in your webi report
and when you change the selection values in filters or input controls then each time you get this error and you have refresh it manually to pull the aggregation values from database as it in Database delegate form due to BICS hence there is a workaround for this as mentioned below .
If you have Plant as an filter or input control then the formula for count would be
= Sum(Count 2011) IN( [ Plant ]) and if you are not using any filters or input controls then try using formula
as =sum(Count 2011) instead of =Count 2011 .
Regards
Jeetan