Hi Jibran
If the WF is working in sandbox, it means that your definition, linkages etc are correct.
Please check if the following note is relevant for you or not:
1770720 - PO workflows run into error SFW_RUN594 - Import container contains errors
It's about correcting the settings in SWEC and SWE2 (correct for your custom workflow definition)
If not, then confirm with your MM consultant if the release strategy is configured correctly or not....take hints from the following SCN thread:
http://scn.sap.com/message/14682486#14682486
Regards,
Modak