I noticed after upgrading to the latest version of WP, 4.7.1, that I now have a warning at the top of the page for one of my sites. The message is: "Warning: call_user_func_array() expects parameter 1 to be a valid callback, no array or string given in /home/ciportnechestx/public_html/wp-includes/class-wp-hook.php on line 298"

Has anyone seen this issue before before? I have other websites that use the same theme version (v3.7.24) and WP v4.7.1 without this issue. I'm still in the process of troubleshooting plugin compatibility issues but all the plugins are fairly well used between the different sites as well.

Thanks in advance.

I haven't seen it in any of my sites - I would suspect a plugin.

The only other thing I'd ask is are the other sites on the same server? if not there might be a PHP version difference.

I don't think either of the patches would be the cause but you might want to install the two Atahualpa 3.7.24 patches
PATCH 3724-01: Custom Menu/SubMenu issue after upgrading to WP 4.4
PATCH 3724-02: Full width headers cause sticky footer to appear below bottom of page

NOTE: I edited your post and changed the WP versionfrom 7.4.1 to 4.7.1 (grin)

I'm seeing this error as well (albeit on line 286). Since I use the Yoast SEO plugin, and a report of this error turned up in the support forum for that plugin at wordpress.org, I thought I'd provide a link from here to there and note the recommended solution (which I have not yet tested myself.)

Airot Halitov writes:

Add to theme functions.php file:

add_filter( 'wpseo_remove_reply_to_com', '__return_false' );

instead of

add_filter( 'wpseo_remove_reply_to_com', false );

Please advise where in Atahualpa's functions.php would be best to add this code -- and thank you!

if you disable the plugin, does the warning go away? If so I would complain to yoast