[Plugin: WordPress Form Manager] Server Error on activation

When I activate this plugin, I get the following error:
“The website encountered an error while retrieving http://”MY_SITE”/wp-admin/plugins.php?activate=true&plugin_status=all&paged=1&s=. It may be down for maintenance or configured incorrectly.

HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.”

Has anyone else run into this? The plugin works on my local test site, but not on our remote staging site.

http://ww.wp.xz.cn/extend/plugins/wordpress-form-manager/