SPSS Base and SPSS Advanced Models only recognizes frequency weights. If you weight your data with a different type of weight, SPSS will not issue an error message; however, you should be sure that you really want your weights to be treated as frequency weights. Note that if you specify probability weights with a weight by command, some procedures SPSS will round the values of the weights to the nearest whole number and use them as frequency weights. In some cases, the nearest whole number may be zero, in which case you may get a message in your output about this. One exception to this is in the crosstabs procedure. For detail, please read: http://en.statistik-tutorial.de/tutorials/weighting-spss.html