Notify If Blanket PO Exists

Dear SCM Gurus,

Notify If Blanket PO Exists in requisition form doesn't pop up. I have a created a BPA, ASL ,sourcing rule and assign sourcing rule are configured and the purchasing option check box "Notify If Blanket PO Exists" is enabled.

Should I consider some thing else. In one test instance it is working , in another it is not.

thanks in advance

Regards,

Chaks