INFOSET ILLEGAL join conditions

Hi All,

I am trying to create an infoset based on 2 tables,but when I try to join a condition then it says ILLEGAL JOIN,

TABLE1 field is CHAR and

TABLE 2  fiels is NUMC…and i am trying to join this fields(both length's are  the same)

Is there any way out to achieve this join with an ABAP logic ,please provide the logic if any idea..

Thanks,

Bobby