DI Error: (-2028) No matching records found (ODBC -2028)
Normally means item code missing in SAP

DI Error: (-5002) [RDR1.ItemCode] .... Business partner catalog number linked to item not specified as sales item 
The item is not flagged as an item for sale in SAP ( i.e. might be purchase item) 
Action: Check the itemcode on the orderline provided in the Error message

DI Error: (-5002) Invalid contact person code 
The user ( Contact TAB on Business Partner in SAP ) does not exist in SAP. Or the user has been moved from one BP to another, or cancelled incorrectly in SAP. 
Search for the user on ODSNet and check if the user is linked to the correct Account ( Business partner). 

DI Error: (-2028) Invalid BP code [ORDR.CardCode] 
The customer account number can not be found in SAP. 
Action: Check the XML message ( Request Message > View Message), the account code is in the <CustomerCode>-tag
Check in SAP if there is an issue with this account. 
If the account has been de-actived in SAP, the order will fail with this message. 

DI Error: (-4013) Posting period locked
The financial period is closed. This can happen in the beginning of a new period / month or year, or if an order has been placed with a future order date. 
Action: Check the order date on the order in the XML message. 
Action: check with your SAP administrator, and ask them to open the required financial period