[Plugin: Admin Log] Error message in header with WP 3.1

Hi, after activating the plugin I see the following message over the header

Warning: fopen(/xxx/wp-content/plugins/admin-log/admin_log.txt) [function.fopen]: failed to open stream: No such file or directory in /xxx/wp-content/plugins/admin-log/admin-log.php on line 83

Warning: filesize() [function.filesize]: stat failed for /xxx/wp-content/plugins/admin-log/admin_log.txt in /xxx/wp-content/plugins/admin-log/admin-log.php on line 84

Warning: fread(): supplied argument is not a valid stream resource in /xxx/wp-content/plugins/admin-log/admin-log.php on line 84

Warning: fclose(): supplied argument is not a valid stream resource in /xxx/wp-content/plugins/admin-log/admin-log.php on line 85

The plugin works, but obviously i can’t use it ??

Any idea ?
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