Carry out modification comparison for FUNC J_1I7_USEREXIT_CALC_EXC_BASE

Dear all,

i have a concern,i have to implement a user exit in tcode j1iin in the FM J_1I7_USEREXIT_CALC_EXC_BASE .now when i try to bring in change mode it says

Carry out modification comparison for FUNC J_1I7_USEREXIT_CALC_EXC_BASE first. No changes possible

...how do i do the modification comparision. i have checked with SPAU and SE95 tcodes but iam unable to compare.please can anyone provide brief explanation and help?

Thanks in advance,

Naren