Multisite privacy plugin error

I've established a dev version of a multisite install that currently has only 2 sites.

I mainly wanted to use the privacy plugin as a quick way to establish a single password for viewing the dev version of the site.

After installing and choosing settings, and clicking 'update sites', the network admin is now stuck on a page that says:

Applying to sites, please wait...

0 of 1 sites updated

If I view source, there is a little js script that has this line in it, not sure if this is relevant:

Cannot modify header information - headers already sent by (output started at /home/precept8/public_html/dev/wp-content/plugins/sitewide-privacy-options/sitewide-privacy-options.php:101