Cant import WordPress post

Every time i try to import my old blog articles from my old site that uses 2.9.2 to the new one that used 3.0. (I moved the site to a different dictionary on my site) I got this error

“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”