Calling a Synchronous Event within a Transaction and Handling Failure

DECLARE @Site SiteType
SELECT @Site = site FROM parms

DECLARE @SessionId RowPointerType
SET @SessionId = dbo.SessionIdSp()

BEGIN TRANSACTION 
UPDATE coitem
SET due_date = dbo.CalcDueDate(@Parm1, @Parm2)
WHERE coitem.co_num = @CoNum
AND coitem.co_line = @CoLine
AND coitem.co_release = @CoRelease

SET @MyEventParmId = NEWID()
EXEC InsertEventInputParameterSp @MyEventParmId, 'CoNum', @CoNum
EXEC InsertEventInputParameterSp @MyEventParmId, 'CoLine', @CoLine
EXEC InsertEventInputParameterSp @MyEventParmId, 'CoRelease', @CoRelease

DECLARE
@anyHandlersFailed [tinyint],
@result [nvarchar](4000),
@Infobar [nvarchar](4000)

EXEC @Severity = FireEventSp
@eventName = SetCoitemDueDate',
@configName = 'SyteLine',
@sessionID = @SessionID,
@eventTrxId = null,
@eventParmId = @MyEventParmID OUTPUT,
@transactional = 0,
@anyHandlersFailed = @anyHandlersFailed output,
@result = @result output,
@Infobar = @infobar output

IF @Severity > 0
BEGIN
EXEC RaiseError @Infobar, @Severity
ROLLBACK TRANSACTION END
...
COMMIT TRANSACTION