All plugins up to date. This appears on frontend when viewing post edit form on frontend:-
Warning: trim() expects parameter 1 to be string, array given in /home/tarasheb/public_html/wp-content/plugins/cred-frontend-editor/vendor/toolset/toolset-common/toolset-forms/classes/class.eforms.php on line 990
There are single select fields (checkbox and radio), the only multiple select field is taxonomy and no generic select fields.
I'm not sure when this first arose but definitely in Forms 2.5.2 and 2.5.1.
Any ideas please?
In case of interest: I discovered I had failed to change the slug on a custom field I had created 'from existing custom field' so I had two custom fields with the same slug (I'm surprised the new field saved successfully). Once I had corrected the new field slug, the warning stopped appearing