I have just created a completely new unmodified install of DotNetNuke_04.06.02_Instal to test a problem we had with a modified and cleaned install.

It seems that in order to use a Category list in the Documents module. So in theory you then go to Host - Lists - Add List

However this operation creates an error 
A critical error has occurred.
Object reference not set to an instance of an object.

if you click the link again you get 
An error has occurred.
DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Common.Lists.ListEntries.BindGrid() at DotNetNuke.Common.Lists.ListEntries.DataBind() at DotNetNuke.Common.Lists.ListEditor.BindList(String key) at DotNetNuke.Common.Lists.ListEditor.cmdAddList_Click(Object sender, EventArgs e) at DotNetNuke.UI.WebControls.CommandButton.RaiseClick(Object sender, EventArgs e) at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e) at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

Any ideas or workarounds?