Hi All,
One more tips, i had a same problem after system migration. I did all your suggestions (Role assignment etc..)but no luck.
Even if you don't get popup once enter the RSA1 T-code don't go back, in same page Goto -> Source system -> Right click Source system name in right side -> and click Activate. You will get error message if your source system not connected properly, then follow the error message.
My case Source system RFC is not working due to wrong Host and User name entry. Finally i changed right one and all went well.
Regards,
Vino