I Receive MSG 7707 When Trying To Split A Partition For The Second Time. Why ?

Hi

I am trying to implement a sliding window on a table in SQL Server 2005 but i am having some problem.
I have two tables, "Letture" and "LettureStorico". The first one receives data on a few seconds basis, some thousands of rows each day. The second is the historical record and should store all the records till midnigh of two days before, that is, if today is November 21st, LettureStorico stores rows till November 19th 23.59:59.997.

At some time during morning of each day i want to run a stored procedures that takes the records older than midnight of two days before in "Letture" and switch them as a partition in "LettureStorico"

Here's what i do:

/*----------------------------------------------------------*/
CREATE PARTITION FUNCTION [partizioneLive](datetime) AS RANGE LEFT FOR VALUES (N'2006-11-15 00:00:00')

CREATE PARTITION FUNCTION [partizioneStorico](datetime) AS RANGE LEFT FOR VALUES (N'2006-11-15 00:00:00')

CREATE PARTITION SCHEME [schemapartizioneLive] AS PARTITION [partizioneLive] ALL TO ([PRIMARY])
ALTER PARTITION SCHEME [schemapartizioneLive] NEXT USED [PRIMARY];/*(1)*/

CREATE PARTITION SCHEME [schemapartizioneStorico] AS PARTITION [partizioneStorico] ALL TO ([PRIMARY])
ALTER PARTITION SCHEME [schemapartizioneStorico] NEXT USED [PRIMARY]; /*(1)*/

CREATE TABLE [dbo].[Letture](
[IdLettura] [bigint] IDENTITY(1,1) NOT NULL,
[IdTag] [int] NOT NULL,
[IdGatewayBox] [int] NOT NULL,
[IsEntrata] [bit] NOT NULL,
[Data] [datetime] NOT NULL,
[IsRettifica] [bit] NOT NULL,
CONSTRAINT [PK_Letture] PRIMARY KEY CLUSTERED
(
[Data], [IdLettura] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON schemaPartizioneLive(data)
) ON schemaPartizioneLive(data)

ALTER TABLE [dbo].[Letture] WITH CHECK ADD CONSTRAINT [CK_Letture] CHECK (([Data]>='20061115 00:00'))

CREATE TABLE [dbo].[LettureStorico](
[IdLettura] [bigint] IDENTITY(1,1) NOT NULL,
[IdTag] [int] NOT NULL,
[IdGatewayBox] [int] NOT NULL,
[IsEntrata] [bit] NOT NULL,
[Data] [datetime] NOT NULL,
[IsRettifica] [bit] NOT NULL,
CONSTRAINT [PK_LettureStorico] PRIMARY KEY CLUSTERED
(
[Data], [IdLettura] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON schemaPartizioneStorico(data)
) ON schemaPartizioneStorico(data)

ALTER TABLE [dbo].[LettureStorico] WITH CHECK ADD CONSTRAINT [CK_LettureStorico] CHECK (([Data]<'20061115 00:00'))

/*----------------------------------------------------------*/

Every morning i run a stored procedure that, after dropping the check constraints (i'll recreate the at the end), does the following:

/*-----------------------------------------------------------*/
SET @NewBoundary = dateadd(dd,-1, @dateOfToday)

--this new partition contains the rows i want to switch
ALTER PARTITION FUNCTION PartizioneLive() SPLIT RANGE (@NewBoundary)
--this new partition is empty
ALTER PARTITION FUNCTION PartizioneStorico() SPLIT RANGE (@NewBoundary)

--this works fine, rows are moved
ALTER TABLE Letture SWITCH PARTITION 2 TO LettureStorico PARTITION 2

--these two merges lead to two tables partitioned in two partitions each
ALTER PARTITION FUNCTION PartizioneLive() MERGE RANGE (@OldBoundaryLive)
ALTER PARTITION FUNCTION PartizioneStorico() MERGE RANGE (@OldBoundaryStorico)

/*------------------------------------------------------------*/

Till now, everything is working as expected.
Now, when i try to run the same Stored Procedure " a day later" (NewBoundary moved on 1 day) i receive, when i do the "ALTER PARTITION FUNCTION PartizioneLive() SPLIT RANGE (@NewBoundary)" i receive a 7707 error message:
"Msg 7707, Level 16, State 1, Line 1
The associated partition function 'PartizioneLive' generates more partitions than there are file groups mentioned in the scheme 'schemapartizioneLive'."

How is this possible if i used the "ALL TO [PRIMARY]" and specified which file to use next as in (1) ? Why all this succeeds the first time (when i have 3 partitions) but not the second (again i have just three partitions, i checked) ?

Someone can help me on this, please ?

Many thankx

Wentu