weighting variables

I have to variables (Generation, Gender) that I have to weight them to be similar to the previous year's data. One variable has missing value that i'm not sure how i should handle it. Each time i keep getting the following message:
>Warning # 3211
>On at least one case, the value of the weight variable was zero, negative, or
>missing. Such cases are invisible to statistical procedures and graphs which
>need positively weighted cases, but remain on the file and are processed by
>non-statistical facilities such as LIST and SAVE.

I did it two ways: one is ignoring the missing value and only weighting the valid values, the other is weighting all values including missing against my desired %s, but both of them lead me to the same warning message above, could someone tell me what I did wrong here? thanks!