In order to prevent invoice errors, invoices will lock by client whenever someone is working on an invoice for that client. Whenever a particular client is locked, a lock icon will appear next to invoices for that client to indicate that those invoices cannot be edited at this time. A message will also appear in the lefthand column indicating what clients are locked and who they are locked by. In addition, any clients that are locked will not show when using the Generate Invoices button. 



Once the user has finished editing the invoice for that client and exited out of the invoice, the lock icon will disappear and they will become clickable again.