Error Pomo

I didn’t installed a new plugin or something else.
And it is a multisite. Only in 1 of them i have this error message 4 times:

Warning: Illegal offset type in isset or empty in /usr/local/www/prostorage/kegelspeter815/gscgambiacom/wp-includes/pomo/translations.php on line 72

If i take a look on that line is this the info:
function translate_entry(&$entry) {
$key = $entry->key();
return isset($this->entries[$key])? $this->entries[$key] : false;

Where is that coming form and how to solve?
Many regards,
Peter