| 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 |