Trying to change media settings generated a warning

When I try to change the default image size of my site via Settings > Media, I get a page with this:

Warning: trim() expects parameter 1 to be string, array given in /home/axtran16/axtran.com/wp-admin/options.php on line 147

Warning: trim() expects parameter 1 to be string, array given in /home/axtran16/axtran.com/wp-admin/options.php on line 147

Warning: Cannot modify header information – headers already sent by (output started at /home/axtran16/axtran.com/wp-admin/options.php:147) in /home/axtran16/axtran.com/wp-includes/pluggable.php on line 876

Does anyone know why and what this means? I notice that the new numbers I entered stay on the page, but there is actually no change when I go to my posts and add images (they use the old/original default sizes).

Thanks.