Backend 404 errors after upgrade to 3.9.1

Hello,

Problem site is http://nonprofitmarketingguide.com/resources

After upgrading to 3.9.1 last week, we are encountering a lot of seemingly random 404 errors on the backend. For example, we will add a post or edit an existing post, and the URL will clearly show that we are doing that, but our 404 page will come up (URL still shows WP editing etc.). Usually we can hit back and try again, and get it, but it happens at very inopportune times too, like when clicking save on a post, getting a 404 and losing the post draft. It doesn’t happen all the time, and I can’t seem to find a pattern. Has happened when looking at plugins, when looking for the version number, etc. So far, only backend issue.

So far, I have tried the “save permalinks” trick (no effect).

I contacted our web host, who said/did this:
“Unfortunately, I wasn’t able to find a specific cause for the 404 and time-out errors for your WordPress installation at nonprofitmarketingguide.com/resources. Based on the following error message, I adjusted your FastCGI timeout to 60 seconds, which is a 15 second increase over the old value:

Connection reset by peer: mod_fcgid: error reading data from FastCGI server”

(That had no real effect as far as I can tell)

This is what is currently in the htaccess file FYI, in case that offers any clues:

AcceptPathInfo On

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /resources/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /resources/index.php [L]
</IfModule>

# END WordPress

Also, we have a second installation of wordpress in a different folder on this same domain and I have NOT upgraded that one to 3.9.1 and it is still working perfectly.

Thoughts? Ideas? Help!

Thank you!