I am having same problem..
basically i am used SAP ECC 5.0 IDES .
I have 800 client.
I activated the source system by clicking active on right click option.
when i am trying to load data from r/3 to bw i got the error saying that "transfer structure prefix for source system was not defined".
So i came to know that in RSBASIDOC table, the fied TSPREFIX was not defined for the source system.
so i modified the TSPREFIX column value from null to BA.
I saved it and logged off.
when i gave RSA1 , I got the same message saying that " Entry in inbound table already exists"
So i reverted the changes what i did before.
Still i am getting same problem.
I dont know how to proceed further.
Pls. help me....what i have to do.
Thanks for your help...