Login Creates Error

Form Manager 1.6.49 causes the following error to be logged each time a user logs in:

PHP WarningPOST /wp-login.php
unlink(/nas/wp/www/cluster-1648/ranchresources/wp-content/plugins/wordpress-form-manager/tmp/.) [function.unlink]: Is a directory

Is there a way to resolve this?

Thanks!
~Mike

https://wordpress.org/plugins/wordpress-form-manager/