Give this link a good read.
If it's that plugin then you should be able to get around it by using FTP or whatever file management tools your host provides you with and navigate to
/home/mgowang/public_html/wp-content/plugins/ and delete the
WP-Client directory. Just that one directory and nothing else.
Please make sure you have a backup of that directory first as a precaution.
eval()'d code(1) error bug me though, can you also scan your site with Sucuri SiteCheck?
That's also as a just in case.