WP 4.0 Update broken site Wiki - URGENT help required.

Ok- I'm using the wiki plugin and the members plugins fine for months and yesterday I updated WP to 4.0 and now the wiki pages can not be viewed on the front end. I will enable support access to the site now - can someone PLEASE quickly look at this for a fix. This is a live, commercial site and people are emailing me asking where the wiki has gone!