Passing Variables To EXEC And Stored Prodecure?

In this line, @BaseName varchar(50) is polulated by a cursor that queries a table for names of other databases. In this first example it works as predicted: 

EXEC('SELECT COUNT (IdPartition) FROM '+@BaseName+'..SAVESET SS LEFT OUTER JOIN SavesetStore SSS ON SS.SavesetIdentity = SSS.SavesetIdentity WHERE [IdPartition] = 0 AND StoreIdentifier IS NULL')


If I create this as an SP (I want the output into another table)

CREATE PROCEDURE GetPArtitionItems @BaseName varchar(50),@IdPartition int, @PartitionItems int OUTPUT

AS

SELECT COUNT (IdPartition) FROM ['+@BaseName+']..SAVESET
SS LEFT OUTER JOIN SavesetStore SSS ON SS.SavesetIdentity = SSS.SavesetIdentity
WHERE [IdPartition] = @IdPartition AND StoreIdentifier IS NULL

GO
Declare @PartitionItems int
EXECUTE GetPartitionItems 'evmailboxstore1',0,@PartitionItems OUTPUT      --EvMailboxStore1 is another table in the same database.

I get: Server: Msg 208, Level 16, State 1, Procedure GetPArtitionItems, Line 7
Invalid object name ''+@BaseName+'..SAVESET' 

 In this case the value is not passed into the @baseName-variable. What do I do wrong?

Thanks in advance - Tim Kuhnell