Publish a post using XMLRPC.

Hi guys.
I'm trying to develop publishing post function using XMLRPC for my app.

I use "metaWeblog.newpost" method for post function.
The problem is this post function works well except server response.

I mean If the publishing was successfully finished then I'm supposed to be get post_id from server. But I got some faultString like following.
"Can't call method \"label\" on an undefined value at lib/MT/Entry.pm line 968.\n"

So I had searched with this strings to figure out what is wrong.
And I found one solution for this problem.

The guy who said figured out same issue shared this information.

have to edit /lib/MT/Entry.pm
Below codes
my @ cats = sort {$ a -> label cmp $ b -> label} @ $ cats

to

my @ cats;
eval ( 'my @ cats = sort {$ a -> labelstrong> C MP $ b -> label} @ $ cats ');

But It couldn't resolve my problem.

Anyone knows what is wrong?