a problem with 'function'

I created a function group 'z_function_group' , and then I created a function 'z_test_function'. When I was trying to activate this function, I got this error :

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Program SAPLZ_FUNCTION_GROUP Row 2

REPORT/PROGRAM statement missing, or program type is I (INCLUDE).

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I don't know why. This is a very simple function. Please help me.

Thanks!!!!