I am seeing this in sp-error log

file: /simple-press/sp-api/sp-api-filters.php
line: 1743
function: htmlspecialchars
Warning | htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument

and line after line of this in wp-error log

PHP Warning: htmlspecialchars() [<a href=’function.htmlspecialchars’>function.htmlspecialchars</a>]: Invalid multibyte sequence in argument in /wp-content/plugins/simple-press/sp-api/sp-api-filters.php on line 1743

any ideas?