Popup box upon rejection is not coming in NWBC

All dear Gurus,

We have designed a custom Workflow for Travel. When manager rejects the rejects a popup will appear to justify the reason for rejection. When we do this via NWBC, the popup is not coming when we reject. it simply got rejected without justification. How can we solve it..?

Any have idea on this..?

Regards,

Namsheed