Every single 3rd party font gives me validation serious errors I recently got El Capitan 10.11.6 installed on my MacBook. Now whenever I try to install ANY 3rd party font, they fail font validation in the Font Book app.

The error is always:

1 serious error was found. Do not use this font.

This occurs for ALL 3rd party fonts. Fonts I download from Adobe Typekit. Fonts I download from Google Fonts, etc. Every single one.

Some websites suggest that I go ahead and install the font anyways. I tried this and certain programs become unresponsive. For example Illutrator CC 2015.3 will not even start up (gets stuck at Initializing) but then once I remove the "bad" font, Illustrator works fine again.

What am I missing here? How do I fix this problem?

UPDATE

As requested here is the Validation Error report from installing a font. The only thing I changed is the network path name for the font location (it was on a network drive).

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;array&gt;
    &lt;dict&gt;
        &lt;key&gt;file&lt;/key&gt;
        &lt;string&gt;Nudista Medium.otf&lt;/string&gt;
        &lt;key&gt;path&lt;/key&gt;
        &lt;string&gt;/network/path/nudista/Nudista Medium.otf&lt;/string&gt;
        &lt;key&gt;report&lt;/key&gt;
        &lt;array&gt;
            &lt;dict&gt;
                &lt;key&gt;fail&lt;/key&gt;
                &lt;integer&gt;1&lt;/integer&gt;
                &lt;key&gt;fontname&lt;/key&gt;
                &lt;string&gt;Nudista Medium.otf&lt;/string&gt;
                &lt;key&gt;pass&lt;/key&gt;
                &lt;integer&gt;0&lt;/integer&gt;
                &lt;key&gt;ruleslist&lt;/key&gt;
                &lt;array&gt;
                    &lt;dict&gt;
                        &lt;key&gt;author&lt;/key&gt;
                        &lt;string&gt;com.apple.ATS&lt;/string&gt;
                        &lt;key&gt;kATSFontTestDescriptionKey&lt;/key&gt;
                        &lt;string&gt;This font has failed one or more of a series of tests of the font interacting with OS X. If you use this font, you may experience text problems or application crashes. Please contact your font vendor for a repaired version of this font.&lt;/string&gt;
                        &lt;key&gt;kATSFontTestNameKey&lt;/key&gt;
                        &lt;string&gt;System Validation&lt;/string&gt;
                        &lt;key&gt;result&lt;/key&gt;
                        &lt;false/&gt;
                        &lt;key&gt;severity&lt;/key&gt;
                        &lt;string&gt;ERROR&lt;/string&gt;
                        &lt;key&gt;version&lt;/key&gt;
                        &lt;integer&gt;65536&lt;/integer&gt;
                    &lt;/dict&gt;
                &lt;/array&gt;
                &lt;key&gt;run&lt;/key&gt;
                &lt;integer&gt;1&lt;/integer&gt;
                &lt;key&gt;warn&lt;/key&gt;
                &lt;integer&gt;0&lt;/integer&gt;
            &lt;/dict&gt;
        &lt;/array&gt;
    &lt;/dict&gt;
&lt;/array&gt;
&lt;/plist&gt;
I've been having the same problem. What has worked for me has been to install an app called Typelight. I go into Typelight, open the font that I downloaded to my computer but didn't install yet, and then save the font to my DESKTOP. It doesn't work if I save it anywhere else, don't ask me why. After that, I open the font by clicking on it on my desktop, then I click "install", and it works with no error messages. More of a hassle, yes, but at least it's a way around the problem.