When an invoice with errors is posted, the message "Invoice XXX created but not forwarded to Accounting" indicate that the document is saved in status "To Be Corrected Manually" and must be processed later to solve the errors and forward to accounting. This is standard in SRM process.
The invoices received in the company must be introduced in the system without any change. SRM must allow the creation and save of the invoices although errors generated by SRM or ECC.
The employees can only enter invoices for purchase orders for which you are either the requester or the goods recipient for at least one item.
The accountant or purchasing assistant can enter own invoices and those of other employees, that is, also invoices for purchase orders for which are neither the requester nor the goods recipient.
The employees and invoicers usually does not have the knowledge / authorization to solve the errors. The system allow to "post"/save the invoice in order to be processed further by an accountant / purchaser to edit the invoice.
If the employee / purchaser post an invoice with errors, the system will save it in status "To Be Corrected Manually". If the users need to really post the invoice(and have the authorization), the check must be executed to confirm that there is no error to be posted and forwarded to accounting
If the invoice is posted with errors, the accountant team will receive a workflow, will use the search for invoices in status "To Be Corrected Manually" or execute Invoice Management System (IMS) to edit the invoices, solve the issue and post the invoice to be paid
Invoice information in help.sap.com: Invoice Management System help 7.0
Invoice Management System (IMS)