ok I'm having a problem with my code that I am using to try and log changes to another table in tblUsageLog (explanation below code in bold)

Code:
-- Will update or insert document information into tblApplicationDocuments
CREATE PROCEDURE dbo.usp_UpdateAppDocs
(
	-- The user ID is required, so it can be added to the usage log
	@pkUserID			int,

	-- The application number
	@AppNumber			int,
	
	-- The date and time the status changed
	@DateStatusChanged	datetime
)
AS

SET NOCOUNT ON

-- Log the updated documents
INSERT INTO tblUsageLog
(
	fkApplicationNumber,
	DateTimeOfAction,
	fkUserID,
	Description
)
SELECT
	@AppNumber,
	@DateStatusChanged,
	@pkUserID,
	'Changed ' + logInfo.DocumentName + ' from ' + logInfo.OldDocumentStatus + ' to ' + NewDocumentStatus
FROM
(
	SELECT 	
		DocumentName,
		DocumentStatus OldDocumentStatus,
		(
			SELECT DocumentStatus
			FROM tlkpDocumentStatuses
			WHERE pkDocumentStatusID = S.fkDocOrTaskStatus
		) NewDocumentStatus
	-- Alias D is for "Destination", Alias S is for "Source"
	FROM qryApplicationDocuments AS D JOIN #temptblApplicationDocuments AS S
		ON D.fkApplicationNumber = S.fkIdNumber
		AND D.fkDocumentID = S.fkDocOrTaskID
	WHERE
	(
		(D.fkDocumentStatus <> S.fkDocOrTaskStatus
		 OR (D.fkDocumentStatus IS NULL AND S.fkDocOrTaskStatus IS NOT NULL)
		 OR (D.fkDocumentStatus IS NOT NULL AND S.fkDocOrTaskStatus IS NULL))
		AND fkApplicationNumber = @AppNumber
	)
) logInfo
When D.fkDocumentStatus IS NULL and S.fkDocOrTaskStatus IS NOT NULL it does not insert a new record tblUsageLog.

It works perfectly fine for where there are no NULL values, but the values are different. Any suggestions?

tblApplicationDocuments:
Code:
CREATE TABLE [dbo].[tblApplicationDocuments] (
	[pkApplicationDocumentID] [bigint] IDENTITY (1, 1) NOT NULL ,
	[fkApplicationNumber] [int] NOT NULL ,
	[fkDocumentID] [int] NOT NULL ,
	[DateReceived] [datetime] NULL ,
	[fkDocumentStatus] [int] NULL 
) ON [PRIMARY]
qryApplicationDocuments and #temptblApplicationDocuments pull off the same basic structure as above except qryApplicationDocuments pulls in some additional plain text based on foreign keys in addition to every field tblApplicationDocuments has and #temptblApplicationDocuments has some fields renamed.

tblUsageLog:
Code:
CREATE TABLE [dbo].[tblUsageLog] (
	[pkUsageLogID] [int] IDENTITY (1, 1) NOT NULL ,
	[fkApplicationNumber] [int] NULL ,
	[fkBrokerID] [int] NULL ,
	[DateTimeOfAction] [datetime] NOT NULL ,
	[fkUserID] [int] NOT NULL ,
	[Description] [varchar] (500) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL 
) ON [PRIMARY]