cause of this error
 

wondering what the cause of this error might be

Warning: Invalid argument supplied for foreach() in [path]/includes/functions_editor.php on line 710

Hard to tell from the little you posted. Since it doesn't happen with default vbulletin, I'd have to guess it is from a modification.

Try disabling your modifications/plugins and see if you still have this problem.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php

ok i will try that...

this error always pops up when i create a new thread or post reply to a thread

**also tried your suggestion and it still shows up.

What is on line 710 of your functions_editor.php file?

Create a new style with no parent:

* Styles & Templates > Style Manager > Add New Style
* Parent Style: No Parent Style
* Title: Default vBulletin
* Allow User Selection: Yes
* Save

Then browse the site using that totally default vbulletin style - do you still have the same problem?

i figured it out. when i upgraded it somehow forgot the includes/xml folder. once that was in it fixed all issues that was hapening