error in call function statement

hi,

i have defined a function with one of the "tables" parameter as shipto_xxx.

in my calling prorgam , i say

call function "zzzz"

tables

shipto_xxx = yyy.

where yyy is a similar structure to hold the data received by the function module.

when i compile i get the error "The field shipto_xxx is unknown but there is a similar field " *shipto_xxx".

why ?