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Check if you didn't forget to copy the class file mentioned in the exception code to $JAVA_TOP.
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oracle.apps.fnd.framework.OAException: Could not create Java class: (xx.oracle.apps.ap.invoice.request.webui.XxInvoiceRequestPGCOExt7) associated with region: (InvoiceRequestPGLayout). This is probably because the class name is wrong or not included in project.