This happens only under specific circumstances.  The base list must have a required lookup column/field that is multi-value.  The view must not include this column.

A required, multi-value lookup column is created to demonstrate the problem:

An example of the list data in standard view, showing the “Region” column:

I created a new view without the “Region” column to show the duplicates bug.  Standard view appears normal:

Same view, but when switched to Datasheet view, duplicate records show:

Same view in Export to Spreadsheet shows duplicates:

If the column is not required, everything works fine.  If the column exists in the view, everything is fine.  It is only when the required column is omitted from the view that you see duplicates.

If the column is included from the view, everything is normal during Edit in Datasheet mode:

Duplicates are now gone in Export to Spreadsheet as well:

There seems to be no fix for this problem.  The work-around is, if you have a required multi-value lookup column, to always add the column to views, especially datasheet views.  If a user creates their own view without the column, they may run into this problem.  User education is the only solution in this case.

Although this seems like a rare circumstance, it does appear that multiple SharePoint users are encountering this problem.  This affects both WSS 3.0 and MOSS 2007.

If, somewhere in the site author tree, you have user accounts that no longer exist, you will encounter the “User not found” error while viewing the report and browsing the list of shared data sources.

I found two good blog articles about this issue as well as a solution here:

• Wherefore Art Thou Author?
• Resetting the Author on a SharePoint site, or Wherefore Art Thou Author Redux

I modified the code a bit to just show the site author without resetting it.  I also changed the code to explicitly dispose of the SharePoint objects.

The utility takes two parameters, the first is the site URL.  If you only pass one parameter, it looks up the site author.  If you pass a second parameter (in the format of DOMAIN\USER), the site author will be reset to the value you supply.

To build, run this from the command-line:

%WINDIR%\Microsoft.NET\Framework\v2.0.50727\csc /target:exe /out:SPResetAuthor.exe SPResetAuthor.cs
/reference:"%COMMONPROGRAMFILES%\Microsoft Shared\web server extensions\12\ISAPI\Microsoft.SharePoint.dll"

Source code of SPResetAuthor.cs:

using System;
using System.Text;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration;

// Original code from: http://blog.krichie.com/2008/09/12/
//      resetting-the-author-on-a-sharepoint-site-or-wherefore-art-thou-author-redux/

namespace SPResetAuthor
{
  class Program
  {
    static void Main(string[] args)
    {
      if (args.Length < 1)
      {
        StringBuilder sb = new StringBuilder();
        sb.Append("\nSYNTAX: SPResetAuthor.exe (Site URL) [new owner]  \n");
        sb.Append("\nwhere:\n\n");
        sb.Append("\n\t(Site URL) - The web URL for"
            + " the site i.e. http://sharepoint/site/");
        sb.Append("\n\t[new owner] - The login account"
            + " for the new author, i.e. DOMAIN\\USER");
        Console.WriteLine(sb.ToString());
        return;
      }
      // Open the site collection
      Console.WriteLine("Opening site collection for: {0}", args[0]);
      using (SPSite site = new SPSite(args[0]))
      {
        // Open the web via the URL passed in
        Console.WriteLine("Opening site (web)...");

        using (SPWeb web = site.OpenWeb())
        {
          Console.WriteLine("Site (web) title: " + web.Title);
          if (args.Length == 1)
          {
            Console.WriteLine("Attempting to retrieve author for site");
            try
            {
              Console.WriteLine("web.Author: {0}", web.Author.ToString());
            }
            catch (Exception ex)
            {
              Console.WriteLine("Exception occured:\n{0}", ex.ToString());
            }
          }
          if (args.Length == 2)
          {
            Console.WriteLine("Resetting Author to: {0}", args[1]);
            SPUser user = web.EnsureUser(args[1]);
            web.Author = user;
            web.Update();
            Console.WriteLine("Author for site {0}, reset to {1}", args[0], args[1]);
            Console.WriteLine("Author ID: " + web.Author.ID.ToString());
            Console.WriteLine("Author Name: " + web.Author.Name);
          }
        }
      }
    }
  }
}

The end result looks something like this:

:

Basically, you just create a new calculated column in the list.  My original column was a DateTime called “Published”.  I created a new calculated column called “Published Month”, type of “string”, with a value of =TEXT(Published,”yyyy-MM”)

After creating the calculated column, just set the “Grouping” for the list. One caveat is that your calculated column is going to be sorted on as well, so it must be in the proper order. For example, the format string “yyyy-MMM”, which produces “2008-Apr”, sorts alphabetically, instead of in date order.

Update: I also found a basic SharePoint calculated field reference, if examples aren’t your thing.

I wanted users to use the standard date-picker, but there is no way to format the date inside the query.  My work-around is a classic Reporting Services pattern – create an internal parameter that does the formatting for you.  The format string for VBScript is “yyyy-MM-ddTHH:mm:ss”.

Below is a screenshot of the Report Parameters dialog. I used the following code to just grab today’s date (no time).

     =CDate(CDate(Now()).ToString("MM/dd/yyyy"))

For the second parameter, I create an internal parameter that is dependent on the first.  This will prevent it from showing on the report and it will not be filled in until the start date is chosen.  Default value:

     =CDate(Parameters!StartDate.Value).ToString("yyyy-MM-ddTHH:mm:ss")

I created a test report to show how this works.  Here is the report definition:

Below is the report preview:  You can now use the parameter in your CAML query.

One other note on CAML date fields.  The time is ignored by default.  If you want to include the time, you must specify another attribute.  Example:

<Geq>

<FieldRef Name="LastModified" />

<Value Type="DateTime" IncludeTimeValue="TRUE">@LastModified!</Value>

</Geq>

I found a helpful post on CAML & DateTime that might be useful for you too.

One difference between them – the names of the Application Pool that SharePoint was running under.  In development it was just “spsite” but in production it was “www.spsite.com”.

I renamed the application pool and *poof*, the site began to work.  I don’t understand the mechanism, but just thought I’d post in case someone else out there encounters it.

UPDATE: I’ve blogged about another reason why you might get the “User not found” error and possible solutions.