"Last delta request loaded in data target is too old: less than 1000 requests found"
One of the pre-condition is that only requests up to the oldest delta requests that were loaded to this data target can be reduced.
In order to analyse and to find out the inbound or outbound delta upload transaction RSREQREDUCE is very useful.
e.g. into infoprovider DSO_1 three different DTP are uploading data in delta update mode:
In that case one SID is very low. Call the manage screen of the infoprovider mentioned in column 'Name of Source Object for a DTP' and check if there are requests which have not been uploaded to the target since a long time. Use the button 'Request retrieved from Infoprovider'
Copy and paste the request which will be displayed when using the button, call transaction RSRQ in oder to identify the SID of the request. In the example above the highest SID 11534148 has been uploaded with SID 11,545,110.
Afterwards you can check e.g. in table RSICCONT if there are more than 1000 request available until request 11,545,110 and the timestamp which has been selected for the reduction.