ora-06531:Reference to uninitialized collection when responding to supplier changes in Purchasing

Hello ,

We are on 12.1.3  and use Purchasing and iSupplier Portal .

Since we upgraded to 11g database we have started noticing an intermittent error ora-06531:Reference to uninitialized collection when buyers respond to supplier changes and enter the response as Accept in purchasing using the navigation :

Purchase Orders>Pending Purchase Order Changes >This screen shows you the list of orders pending supplier changes>click on a PO>Click on Respond to changes>Enter response as Accept>Submit>The error above comes up once in a while We are unable to replicate this in test .The workaround we have to use is enter the response as Reject and have the supplier resubmit the changes and then have the buyer accept the changes.