Hi Prasad,
I don't know the ole db task maybe you're on 10 version (I'm working on 7.5 and the system variable for appset in BPC is simply %APPSET%) but if @bpcappset is your system variable try setting on bpc package a global variable
GLOBAL(MYAPPSET,%BPCAPPSET%) then you can use it in your exec instruction
EXEC ProcName @MYAPPSET
Regards
Roberto