Alright. Step one yielded this result on every post and every page:
Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'gallery_columns' was given in /home/wings/public_html/wp-includes/plugin.php on line 166
Checking line 166 gave me this:
do {
foreach( (array) current($wp_filter[$tag]) as $the_ )
if ( !is_null($the_['function']) ){
$args[1] = $value;
$value = call_user_func_array($the_['function'], array_slice($args, 1, (int) $the_['accepted_args']));
(Dreamweaver lists line 166 as $value = call_user_func etc etc)
So it’s something server side I don’t understand. Should I proceed with your suggestion of turning each back on until I find the culprit, or has it just revealed itself? For reference, I have the Gallery Widget plugin as well (but that seemed to be working). I’m thinking it may be the problem, but I’m probably wrong.