Can't access WP-Admin – blank white screen

A client mailed me today that she could not log-in to WordPress.
When I went to the wp-admin, I didn’t even get to the login part, I just got a blank page.
I have searched the forum and the rest of the internet and tried several of the solutions found there.
So far I have the admin part working again, but ONLY if I deactivate certain plugins that I do need.

The site itself did work with those plugins activated, but not the admin part.
I have manually updated WordPress, that didn’t help.
The plugins that I now have turned off are:
– All in one SEO Pack
– Autochimp
– Mailchimp
– Page links to
– Reveal IDs
– WP Js List Pages Shortcode
If I activate any of these, I get the blank screen again

and then there is 1 plugin that I cannot update, because then it triggers the blank admin-page as well:
– WP-Supersized

other plug-ins that are activated now are (just in case one of those might be the problem)
– Exclude pages from navigation
– Executable PHP Widget
– Latest twitter sidebar widget
– TinyMCE Advanced
– User Role Editor
WP-supersized (older version)

HELP!!
I really hope for someone that will & can help me.