I would say 90% of the errors people get with MLM is uploading lists. This forum is full of entries related to that issue. Unfortunately that comes from the server. It be caused by a mod_security Access denied error. Create a '.htaccess' file in the script directory with the following text:
<IfModule mod_security.c>
SecFilterEngine Off
SecFilterScanPOST Off
</IfModule>
or just:
SecFilterEngine Off
SecFilterScanPOST Off
More information on this here:
What is mod security and how does it affect me.
Another possible solution is to create your own 'php.ini' file, inside the 'lm' folder, that will override certain php important variables. Add the following to that file:
upload_max_filesize = 20M;
post_max_size = 20M;
register_globals = On;
allow_url_fopen = On;
memory_limit = 24M;
max_execution_time = 1800;
max_input_time = 1800;