Problem:
[ArgumentException: ERROR CREATING CONTROL FOR NODETYPE: Media]
umbraco.cms.presentation.Create.Page_Load(Object sender, EventArgs e) in d:\inetpub\wwwroot\ccnet\Source\Umbraco 3.1\umbraco\presentation\umbraco\create.aspx.cs:45
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
System.Web.UI.Control.OnLoad(EventArgs e) +99
umbraco.BasePages.BasePage.OnLoad(EventArgs e) in d:\inetpub\wwwroot\ccnet\Source\Umbraco 3.1\umbraco\businesslogic\BasePages\BasePage.cs:287
System.Web.UI.Control.LoadRecursive() +50
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

Solution:
1. open the UI.xml (located in /umbraco/config/create
2. search for the node with alias ‘media’,
3. change the alias in ‘Media’ (first letter a capital).
4. save the UI.xml
5. restart the website (to make sure the new UI.xml is loaded.