UPDATE( SAPUP50R) to update table of custome infotype ,subroutine abnormal

hi,

I am using

PERFORM UPDATE(SAPUP50R).

to update database table pa99XX of a custom infotype ,

this works fine when used in the report program , but the subrioutine UPDATE(SAPUP50R) fails to update the database table when used inside a functional module.

pls help me.

thanks ,

avakash.