| A1 | The Interconnect Mailbag Acknowledgment Count is Not Equal to the Actual Interconnect Mailbag Acknowledgment Count |
| B1 | The Interconnect Mailbag Interchange Count is Not Equal to the Actual Interconnect Mailbag Interchange Count |
| C1 | The IH and IT Mailbag Header and Trailer Control Numbers Are Not Identical |
| D1 | Invalid Interconnect Mailbag Version Number |
| E1 | Invalid Interconnect Mailbag Logon ID |
| F1 | Invalid Interconnect Mailbag Password |
| G1 | Invalid Interconnect Mailbag ID Qualifier Code |
| H1 | Invalid Interconnect Mailbag Sender ID |
| I1 | Invalid Interconnect Mailbag Receiver ID |
| J1 | Invalid Interconnect Mailbag Date |
| K1 | Invalid Interconnect Mailbag Time |
| L1 | Invalid Interconnect Mailbag Time Code |
| M1 | Invalid Interconnect Mailbag Test Indicator |
| N1 | Invalid Interconnect Mailbag Action Code |
| O1 | Invalid Interconnect Mailbag Error Code |
| P1 | Invalid Interconnect Mailbag Control Number |
| Q1 | Invalid Interconnect Mailbag Acknowledgment Count |
| R1 | Invalid Interconnect Mailbag Interchange Count |
| S1 | Invalid Interconnect Mailbag Data Element Separator |
| T1 | Invalid Interconnect Mailbag Segment Terminator |
| U1 | Invalid Interconnect Mailbag Segment Type |
| V1 | Missing or Partial IT Segment Detected |
| W1 | Duplicate Mailbag Control Number for this Sender |
| X1 | Unrecognizable Interconnect Mailbag Contents |