Program Exits in Activity step is triggering 7 times in Subworkflow

Dear Experts,

I have created a subworkflow in which i have added an activity step, created a task for BUS2250-Validate method and written my code in programe exit to send mail by creating a class for interface IF_SWF_IFS_WORKITEM_EXIT and inside method IF_SWF_IFS_WORKITEM_EXIT~EVENT_RAISED i have written my code.

Now the problem is that whenever i run my subwworkflow alone, the code is getting executed again and again so getting mails 6 to 7 times.

What should i do now??

kindly suggest.

Thanks

Kavya.