Yes, I checked by wireshark on client side, params is send correctly. Then I use Webmin function ReadParse and this function return me the %in variable with correct data. But I don't use ReadParse because different problems with this function :D Data is incoming correctly, there were must be problem with CGI function (maybe some limit?). I don't know why the function return me only 834 values of checkboxes, why not 1000 :-(.