after weeks of struggle, i found a solution for those who can’t import your mt text file to your wordpress. pardon my english, i’m mexican.
i wanted to import a blog from bitacorae (bitacoras.com) to wordpress 2.0.2, who used an export system similar to movable type. but when i used the import form first it got into issues with the time of upload of the file (maximum time exceeded, blah blah), and then, when i decided to cut the text file into pieces, the “bad arguments” and “implod” warning started (like in this thread). i was desperate because this fellow of mine has a big audience and we needed to migrate everything before july the 2nd, the day of presidential elections in mexico.
so i found a script/newimport form from trac. at the bottom of the script there’s a download link. save it in your pc and rename it import-mt.php. upload it in your wp-admin directory.
access it from your browser and follow instructions. you’ll have to upload your text file into wp-admin and edit just one single bit of the huge script so it locates the file in your server.
it will recover your mt posts, your mt comments and your mt categories (minor issue on displaying categories on the blog, but they appear in the manage tab).
original blog: https://goleech.bitacoras.com
wordpress blog: https://goleech.enmonterrey.com
i don’t know what’s with that script and why it’s not publicly available, but it worked for me and i’m almost crying, ha.