Export file is empty

Hi there,
I am exporting my sites settings through
Tools / Export and then trying to import it to another wordpress site I own using the WordPress Importer plugin.
I choose the exported file and hit Upload but the following error message appears:

Sorry, there has been an error.
File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.

I have already modified the max upload size in the php.ini file and has not worked. I think the problem is in the exporting of the file, as it is only 113 kb for a blog with a whole structure created on it.
Any solution on this? Have google it but nothing comes out.
Thanks