Hi Pranay,
Thanks for your input.
I have tried this as well:-
Goto tcode SE41, enter program name as 'SAPLFI_ITEMS' and click on copy user interface push button (CTRL+F5).
A popup will appear, enter 'SAPLZFI_ITEMS' in 'To Program' and click ok.
But, here, the error message appears:-
"Interface SAPLZFI_ITEMS already exists"
After activation, I tested it anyway and the menu options are still disabled 
Any other ideas?
Regards,
Deborah