If you plan on using Microsoft AJAX with web services, you better plan hard. The AJAX Control Toolkit is currently built using web services. I attempted to use the NumericUpDown control provided in a user control. However, I continually received an error message stating that "The given key was not present in the dictionary." Upon further investigation, I found that the partial pages in the code samples inherited the CommonPage class. The CommonPage class, found in the App_Code folder, inherited the Page class. The page class contains some additional events in the load cycle that the user controls do not contain such as Pre_Init. In the CommonPage class, there is an override for PreInit which grabs all content placeholders and adds them to a list. That was it, once I switched the contents from a user control into a page, it worked. Of course there are other work arounds to get the User Control to pull the content place holders.