404 Error When Trying to Create New Banner Client - Joomla! Forum - community, help and support

when try create new banner client or category, 404 category not found error web address of (domainname)/administrator&itemid=1

debug info follows:

call stack
# function location
1 jsite->dispatch() path/public_html/index.php:42
2 jcomponenthelper::rendercomponent() path/public_html/includes/application.php:197
3 jcomponenthelper::executecomponent() path/public_html/libraries/joomla/application/component/helper.php:351
4 require_once() path/public_html/libraries/joomla/application/component/helper.php:383
5 jcontroller->execute() path/public_html/components/com_content/content.php:16
6 contentcontroller->display() path/public_html/libraries/joomla/application/component/controller.php:760
7 jcontroller->display() path/public_html/components/com_content/controller.php:74
8 contentviewcategory->display() path/public_html/libraries/joomla/application/component/controller.php:721
9 jerror::raiseerror() path/public_html/components/com_content/views/category/view.html.php:56
10 jerror::raise() path/public_html/libraries/joomla/error/error.php:251

i designer, not skilled developer. please make replies newbie friendly. can change code if given file path , code replace with. thank in advance assistance may provide!

here's link troubleshooting common joomla error, there's section on 404 errors @ bottom.

http://www.siteground.com/tutorials/joo ... issues.htm