Can't mkdir in mounted directory - so no cache is created

Hi

I just moved the home directory to a mounted drive and then Boost stopped functioning. The error report says : Permission denied in boost_mkdir() (line 1407 of /B64/home/bjarstal-com/public_html/sites/all/modules/boost/boost.module).

on 1405 to 1414 we'll find this

// Try to create the directory.
$mode = variable_get('file_chmod_directory', 0775);
if (!mkdir($directory, $mode, TRUE)) {
watchdog('boost', 'Could not create the directory %dir on your system', array('%dir' => $directory), WATCHDOG_ERROR);
return FALSE;
}
drupal_chmod($directory);
}
return TRUE;
}

What is this about??

All the best

Hans