Dear Ajith,
what are the system details of the Netweaver 7.4? It's SAP_BASIS and Kernel version and patch details.
Is it only transaction ME21N that you have this issue with the 'ENTER' key? Or do you get the same behaviour with other transactions that use the same control?
What type of control are you using? Can a screenshot be attached?
See the note
2165116 - Tablecontrol: ENTER key has no effect
Regards,
Oisin