Value does not fall within the expected range

Question

SPWeb web = SPContext.Current.Web;

            SPSiteDataQuery query = new SPSiteDataQuery();

            query.Lists = "<Lists>" +
                          "<List ID=\"" + web.Lists.TryGetList("StaffNews").ID.ToString() + "\" />"+
                          "<List ID=\"" + web.Lists.TryGetList("CompanyNews").ID.ToString() + "\" />"+
                          "<List ID=\"" + web.Lists.TryGetList("ManagementNews").ID.ToString() + "\" />" +

                          "</Lists>";

            Guid listItemId = new Guid(HiddenFieldID.Value);

            DataTable dt = web.GetSiteData(query);

                list["Nickname"] = TextBoxName.Text;
                list["_Comments"] = TextBoxComment.Text;
                list.Update();

Answer 1

Possibly, in addition to C.Marius answers you should wrap ID with " marks. So instead of

"<List ID=" + web.Lists.TryGetList("StaffNews").ID.ToString() + " />"

write

"<List ID=\"" + web.Lists.TryGetList("StaffNews").ID.ToString() + "\" />"

Answer 2

I'm sorry but your code is quite faulty. You do a list loop (all Lists in the current Web) and then try to update one particular SPListItem by with what ID??

//this retrieve a LIST Item, start with a listItemId created from what??
SPListItem itemToUpdate = list.GetItemByUniqueId(listItemId);

You should really review what are you trying to achieve, because the code it doesn't entirely make sense.

[EDIT] - As it seems you are trying to update all result across the 3 specified list after retrieving results using SPSiteDataQuery. In order to achieve that you need:

1. Use SPSiteDataQuery but also include the UniqueId as return field
2. Use the resulting DataTable to loop through the rows while retrieving the SPListItem based on that UniqueId (at this step SPList is no longer needed, because using the paretn SPWeb it could easily achieved)
3. Perform the update.

See here to get you started up to the point where DataTable is populated http://chakkaradeep.com/index.php/retrieving-an-item-from-the-rootweb-and-subwebs-using-its-uniqueid

Answer 3

Adding a Stacktrace to the output will help to find the error.

Just add

    catch (Exception x)
    {
        LabelComment.Text = x.Message + x.StackTrace;
    }

See: http://msdn.microsoft.com/en-us/library/system.exception.stacktrace(v=vs.90).aspx for more information on the StackTrace property.