Would it be possible for you to make the avi file in question avaliable?

mhhhh....
1st this seems to happen to all files
2nd the avi is too large (190 MB)

but I tried to write a test script:
<?php 
var_dump(mime_content_type('/home/e05/file1.avi'));
print "<hr>\n";
var_dump(mime_content_type('/home/e05/file2.mov'));
print "<hr>\n";
var_dump(mime_content_type('/home/e05/file3.zip'));
print "<hr>\n";
var_dump(mime_content_type('/home/e05/file4.rm'));
print "<hr>";
 ?>
The intresting point seems to be the output.
Warning: mime_magic: invalid type 0 in mconvert(). in /home/ck/lamp/public_html/filemanager/bugtest1.php on line 2
(repeats about more than hundred times each line with a mime_content_type call! while ignoring print "<hr>\n";)

the end is that the last mime_content_type returns a value after a lot warnings:
string(19) "application/x-troff"
The only print "<hr>\n"; that seems to be executed works there.

Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions. 

Thank you for your interest in PHP.

Sounds like a problem with your magic file used by the mime_magic extension.

well, it sounds like the mistake is mine but the error message is not really usefull :(
I would preffer an error message that says "Hey, you?ve got a problem magic file" (well, something like that; And I have to check that)
But the error messages is really useless!