Hi,
We have faced the similar error some time back .Check the below.
go to sld -->Business systems-->select your ECC business system and click on Integration tab-->check every thing is fine (client,logical system,technical system ...).
If the above are fine then come to ID and click on your Business system-->adapter specific identifiers-->check is it the same as BS in sld ? If it is not the same then click on icon at bottom(compare with sld) to reimport .
Regards
Venkat