I faced a problem with the menu item "Web services". I tried to add a 3d party module, but I couldn't do that because in my admin menu System I couldn't find the "Web services" menu item. I already check all models, controllers, and config XML files. All the same as in default Magento installation. I have not any modules that can impact on that menu. Also, SOAP installed and enabled.
I've fixed this problem.
- Got to the "app\etc\modules"
- Find files Mage_Api.xml Mage_Api2.xml Mage_Oauth.xml
- In these files, you need to change false to true
- rebuild Magento cache