how to add more .bro files in bro?

When I want to use more .bro files, such as:
   ./bro -i eth0 ftp.bro http.bro,
then the program tell me that it can't go on when it analy the http.bro.

How exactly does it tell you that "it can't go on"? Because the above
should work (assuming you don't in fact have a comma after "http.bro");
or, more specifically,

  ./bro -i eth0 mt.bro http.bro

should work.