Fatal Error - Website down!

I have a live site currently down with the message:

{!– ra:00000000638f5ffd00000000469f18aa –} Fatal error: Cannot use object of type stdClass as array in /xxx/system/expressionengine/libraries/Functions.php(688) : eval()’d code on line 33

Added a channel entry yesterday and I know the site worked fine after that yesterday afternoon. This morning the site was down with that error so no obvious cause.

The admin section still works, running ExpressionEngine v2.9.2