Does the content in question have any img tags?

Can you change line 1357 from

if ( $qp->length == 0 ) {

to

if ( ! $qp->length  ) {

and report if the error is still encountered.

Nothing changed.

if ( $qp->length == 0 ) { is line the 1348

The relevant part is the following:

if ( empty( $img->attr('title') ) ) {

$title = str_replace('_', ' ', basename($src));
 $img->attr('title', $title);

}

If I comment out this if then it works.

Has there been any progress on this issue? I am experiencing the same issue on a fresh installation of mediawiki 1.25.1. I am unable to even load the Special:SpecialPages when the Html2Wiki extension is enabled in my LocalSettings.php. I get the following error in my /var/log/httpd/error.log:
PHP Fatal error: Can't use method return value in write context in /var/www/html/extensions/Html2Wiki/specials/SpecialHtml2Wiki.php on line 1357

Line 1356 - 1359 in the SpecialHtml2Wiki.php file is:

1356 $img->attr('src', $src);
1357 if ( empty( $img->attr('title') ) ) {
1358 $title = str_replace('_', ' ', basename($src));
1359 $img->attr('title', $title);

This is a limitation of the EMPTY() function in PHP versions BELOW 5.5.
EMPTY only will check variables, not return values from functions.

So to fix this, in SpecialHTML2Wiki.php change

if ( empty( $img->attr('title') ) ) {		
    $title = str_replace('_', ' ', basename($src));
    $img->attr('title', $title);
}

to

        
if ($img->attr('title') ) {
    $title = str_replace('_', ' ', basename($src));
    $img->attr('title', $title);
}

OR, in theory you should be able to upgrade your php to 5.5+ to fix this issue. I am running 5.3 and used the above workaround instead of upgrading; YMMV.

Reference StackOverflow page on the underlying issue
http://stackoverflow.com/questions/1075534/cant-use-method-return-value-in-write-context

I love this collective triaging above! Patches are also welcome directly on the repository, see https://www.mediawiki.org/wiki/Gerrit/Tutorial :).

Thanks for the fix. I've committed the suggested fix and will push it
upstream asap (30 minutes). Thanks for using this extension and would love
to hear from users.