Forum Post: Invoice# beginning with "I" as opposed to "G" or "C" - what does it mean?

I recently printed Bill Stage Listing report and a couple of the invoice numbers begin with the letter "I" (eye) instead of the usual "G" for global or "C". Also the numbering of the "I" invoices is in the 30,000s when my regular invoicing is in the 16,000s. What does it mean? How can I fix it?