Issue in PO standard workflow

hello expert,

I am using stanadrd workflow WS20000075 For PO release process .

When i create any PO using ME21N Tcode, The approval process is working fine .

But this error message comes to SAP Inbox

Error processing following event linkage:
BUS2012
RELEASESTEPCREATED WS20000075

Following error occurred:
SWF_BND_001
070
&ReleaseCode&

Message text:
Source expression
'&ReleaseCode&' is invalid
SAP System: ECD
Client:
210

Event container appended as attachment.

Event linkage not
changed.
Event stored temporarily.

Please help to find out the solution for this issue.

Thanks & Regards

Anshul