This sounds like it could be due to the evils of indirect object methods. Firstly make sure that the format() method is being called from an existent object e.g

# this should create an object to work with
my $obj = Some::Module->new();
   # call the format() method on the $obj object
   $obj->format();
[download]

I don't think you really need to go into a debugger at this stage, especially with such a nice and descriptive warning message (which is further explained in perldiag). Perhaps if you just brushed up on your perl skills or read a couple of man pages^[1] then you could crack the case of the missing object.
HTH

_________
broquaint

^[1] check out Masem's excellent How to RTFM for further info on how to take advantage of perl's extensive docs