I had the same issue, and it referenced a call in widgets.php. However, the fix for me was not in widgets.php (as that was a call to Yadis.php).
I followed @blueyed’s solution (which is fixed in the code for WP-OpenID 2.1.7 already):
To fix this for PHP4, replace line 278 (the one causing the error) like this (removing ” = null”):
- function discover($uri, &$fetcher = null,
+ function discover($uri, &$fetcher,
but then to add a memory markup on line 2 of wp-content/plugins/openid/Auth/Yadis/Yadis.php with:
ini_set("memory_limit","12M");
Then everything worked fine.