call_user_func_array() First argument is expected to be a valid callback : theme.inc on line 617

any update on this? I am experiencing the same problem:
warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'theme_filter_tips' was given in /home/specweb/public_html/includes/theme.inc on line 617.

I have the same problem when I click Checkout in the eCommerce Cart.

* warning: Parameter 1 to theme_ec_mail_checkout_form() expected to be a reference, value given in C:\xampp\xampp\htdocs\dp_cms\includes\theme.inc on line 617.
* warning: Parameter 1 to theme_ec_checkout_checkout_review_form() expected to be a reference, value given in C:\xampp\xampp\htdocs\dp_cms\includes\theme.inc on line 617.

It seems it is not a problem related to eCommerce. Any suggestions ?

Drupal 6.14
eCommerce 6.x-4.x-dev
MySQL 5.1.37
PHP 5.3.0

same problem for me

Drupal 6.15, clean installation

Just spotted the same issue by visiting this link (Add menu block):

http://localhost/admin/build/block/add-menu-block

BTW, I don't have "Relevant Content" module installed.

Same problem with Drupal6.15, and only on a new server running PHP5.3 (site migrated from other hosts pre PHP5.3), and for another module:

warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'theme_viewfield_formatter' not found or invalid function name in /Library/WebServer/Drupal/drupal-6.15/includes/theme.inc on line 617.

Very glad for updates.

I am a module author and see this too
I had to locate everywhere I'd called
theme("my_module_thumbnail", $node);
and change to
theme_my_module_thumbnail($node);

I have no idea why, it may be related to PHP5.3 according to http://drupal.org/node/772894#comment-3015910