Same problem here:
Warning: rename(XXXXX.com/wp-content/uploads/XXXXX.jpg) [function.rename]: Invalid argument in XXXXX.com\wp-content\plugins\easy-watermark\classes\class-ew-plugin.php on line 880
Warning: Cannot modify header information – headers already sent by (output started at XXXXX.com\wp-content\plugins\easy-watermark\classes\class-ew-plugin.php:880) in XXXXX.com\wp-includes\pluggable.php on line 1173
