Permalink error: urlencode() expects parameter 1 to be string

Hi Hiroko, 

Sorry for the delay.  I've located the source of this issue.  Can you try this patch in permalinks.php?

Search for $namesToValues and replace this code: 

    foreach ($namesToValues as $name => $value) {
      $_GET[$name]              = $value;
      $_REQUEST[$name]          = $value;
      $_SERVER['QUERY_STRING'] .= "&$name=" . urlencode($value);
    }

With this code:

    // create _GET/_REQUEST values
    foreach ($namesToValues as $name => $value) {
      $_GET[$name]              = $value;
      $_REQUEST[$name]          = $value;
    }
    
    // create QUERY_STRING
    $_SERVER['QUERY_STRING'] = http_build_query($namesToValues, null, '&');
    $_SERVER['QUERY_STRING'] = preg_replace('/(%5B|\[)\d+(\]|%5D)/i', '[]', $_SERVER['QUERY_STRING']); // replace name%5B0%5D, name%5B1%5D with name[], name[]

Let me know if that resolves the issue for you.