Activity type unit measure change after plan price calculation

Hi Guys

Have one issue on Activity type unit measure . early unit measure is "S" i was calculated activity type plan price calculation and run the standard cost estimate-Release also done. now i want to change the unit of measure S into "EA".

But system is throughing error message "Transaction data already exit".

I deleted directly in COST Table level deleted Activity type plant price object. i was try to change unit of measure but still i am getting same error message.

If i will change in master data table level CSLA, what r the implications please give me solution.

Regards

shivaji