Hi,
Check the source system RFC connection in SM59, if this is ok then check the tcode WE20 for EDI partner profiles and inbound and out bound Idocs defined.
In BW Out boud IDOC type should be same in ECC in bound Idoc type, and in ECC out Bound IDOC type should be same in BW in bound IDOC type then the source system activation is possible in RSA1.
