This age old message never contained the information needed to help this guy. There are many reasons why it did not work on the server, starting with where the script is allowed to run (Client, Server, Client+Server) or which events, as not all of them can execute on the server. Click, Enter, Exit, Change etc only work with interactive forms inside Adobe Reader/Acrobat. Also, how did he save the form/render the form. If you create a static print PDF then event execution is different to what it is interactively. Finally, xfa.host.messageBox DOES NOT WORK ON THE SERVER
No problem for two people is exactly the same - so you should provide more details about your form here to get help.