Getting errors with IMGSIZER

Hi everyone

I am getting these errors when I test the template out:

A PHP Error was encountered Severity: Warning Message: mkdir() [function.mkdir]: Permission denied Filename: imgsizer/pi.imgsizer.php Line Number: 200

A PHP Error was encountered Severity: Warning Message: Cannot modify header information - headers already sent by (output started at /Applications/MAMP/htdocs/richardquaydesign_ee/login/core/Exceptions.php:166) Filename: core/Common.php Line Number: 428

here is the code that those errors are coming from:

{med_hero_bottom_image}
                <a href="http://{link}">{exp:imgsizer:size src="{artwork}" width="480" height="176" }{artwork}</a>
            {/med_hero_bottom_image}

Does anyone have any ideas? I had this plugin working with no issues in 1.6.8

Thanks everyone!