Hi Suresh,
Well, at least you know which user it is, Basis/100, and what time exactly it happened every day.
Maybe you can start a trace-by-userid slightly before the time it will happened, and also check where is this RFC came from during that time (dev_rfc log, sm59).
In the meantime, you can change the user-type to either System or Service user, depending if you need to login via SAPGUI or not).
I hope this will help you.
Regards,
Andre