If you are not sharing ( dbprefix_themes )
After being a NEW member ( register.php) for a while error field;
'{db_prefix}themes', smf_themes
Sources/Subs-Members.php
// Theme variables too?
if (!empty($theme_vars))
{
$inserts = array();
foreach ($theme_vars as $var => $val)
$inserts[] = array($memberID, $var, $val);
$smcFunc['db_insert']('insert',
'{db_prefix}themes',
array('id_member' => 'int', 'variable' => 'string-255', 'value' => 'string-65534'),
$inserts,
array('id_member', 'variable')
);
}