Hi Manas,
I guess it might occored due to some patch upgrade you did it recently.As the error suggests the mentioned FM is not in libraray.Check in SE37 whether the same exists.if exist try to regenrate the FM once again.
Also check the recent transports occurred within last 2 days.check any dependent object is transported,Ensure the same FM is not obsolete in ECC 6.0.
Hope it will address your query.