CSS

I have updated to the latest version of this theme. I lost all the css I had put in during the upgrade. Now I am getting the message below in the css box in theme options:

<br />
<b>Warning</b>:  htmlspecialchars() expects parameter 1 to be string, array given in <b>/home/MYSITENAME/public_html/wp-includes/formatting.php</b> on line <b>3438</b><br />

I cannot make any changes to the site. Please advise on a fix.

Thanks