Hi Clifton
I think you would not be able to run RSA1 in OLTP system , unless your RSADMINA table contains an entry indicating that particular client is BW one . SE16 --> RSADMINA --->BWMANDT ( check this OSS note Note 1949194:How to Modify Table RSADMINA )
To delete source system you created by mistake, you have to delete an entry from RSBASIDOC table. There is a function module to do the same ( RSAP_BIW_DISCONNECT) . Please read the relevant note for the same.
But, even with this entry you should be able to create your OLTP system as SAP source system to BW . I am not sure why you are facing problem there because you did not mention the detail. Are you trying to create the source system from OLTP system ? If yes, do it from BW system -->RSA1 --->Source System---->SAP folder ---->Right Click ---->Create.
However, folder does not matter actually. I have seen may ECC source system under BW folder and that still works as expected.
Regards
Anindya