Fatal error escape failed at background-image: colorizeimage

If you see an error message similar to this:

Fatal error: Uncaught Exception: unknown value type: escape: failed at `background-image: colorizeimage(~"@{level@{index}minuscolorize}", ~"@{level@{index}minusimage}", ~"@{level@{index}minuscolor}"); ` line: 67 in /wp-content/plugins/nextend/library/css/less.php

then your problem will be, that your Accordion Menu is not updated, so you should update it.