Hello Maddy
Please go through below SAP notes -
1131469 - DELTAREPORT: unjustified error 181/183 for confirmation
794281 - Locked purchase orders missing from R/3
1022343 - Delta report displays too many errors (181)
817354 - No delete event when you delete orders in APO
Some Old SCN threads -
CCR Error 154 - Planned Order Missing in R3 wit... | SCN
CIF Problem -- Purchase Orders - Missing in R/3 with External Key
This is good document on CCR error handling.
CIF-Comparison / Reconciliation of Transaction Data
Hope this will help.
Thank you
Satish Waghmare