iSupplier: External User: Create Invoice with PO: Error after adding attachments

We are upgrading the applications from R12.1.3 to R12.2.6, while testing iSupplier portal, I encountered an error while creating Invoice with PO as an external user. In the Details Page, select an attachment and Apply and then the page throws below error:

You are trying to access a page that is no longer active.

- The referring page may have come from a previous session. Please select Home to proceed.

Reproduce:

1. Login as an external user

2. From the FINANCE tab, Create Invoice with PO

3. In the Purchase Orders page, Search a PO and then select

4. In the Details, Select Remit To, enter Invoice Number, Invoice Type as Invoice and enter Description. Then, click on Add(attachment). In the Add Attachment dialog box, select a file and then Apply.