Error Converting Data Type Varchar To Int.

can anyone see as to why I would get this error with the following SP?

 ALTER PROCEDURE [dbo].[SP]
@ID int = 0,
@emailFrom VARCHAR(50) = Null,
@emailDate VARCHAR(50) = Null,
@emailSubj VARCHAR(50) = Null,
@emailTxtBody VARCHAR(1000) = Null,
@emailHtmlBody VARCHAR(1000) = Null

AS
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;

DECLARE @Notes VARCHAR (8000)
DECLARE @TicketID INT
DECLARE @emailBody VARCHAR (1000)
DECLARE @Length Int

SET @Notes = ''
SET @Length = LEN(@emailSubj)

-- insert a new entry
INSERT INTO PopEmail
( emailFrom, emailDate, emailSubj, emailTxtBody, emailHtmlBody )
VALUES
( @emailFrom, @emailDate, @emailSubj, @emailTxtBody, @emailHtmlBody )
-- get the new ID
SET @ID = @@identity

If ( @ID <> 0 ) AND ( ISNUMERIC(@emailSubj) = 1 )

Begin
IF @emailTxtBody IS NULL
BEGIN
Set @emailBody = @emailHtmlBody
PRINT '@emailHtmlBody: ' + @emailBody
END

ELSE

BEGIN
SET @emailBody = @emailTxtBody
PRINT '@emailTxtBody: ' + @emailBody
END

SET @TicketID = CAST( @emailSubj AS int )
SET @Notes = @emailFrom + ', ' + @emailDate + ', ' + @emailBody
Select @ID = ID From TicketDetails Where TicketDetails.TicketID = @TicketID

Exec differentSP @ID, @TicketID, @Notes

PRINT 'Subject: [' + @emailSubj + ']'
print 'length: ' + CAST(@Length as varchar (10))
Print 'emailSubj: ' + CAST( @emailSubj AS int )
PRINT 'ID: ' + Cast( @ID as varchar ( 10 ) )
PRINT 'TicketID: ' + Cast( @TicketID AS Varchar ( 10 ) )
PRINT 'Notes: ' + @Notes
PRINT 'ID: ' + Cast( @ID as varchar ( 10 ) )
END
ELSE

BEGIN
Print 'ID: ' + CAST(@ID AS VarChar(10))
PRINT 'ISNUMERIC: ' + CAST(ISNUMERIC(@emailSubj) AS VarChar (10))
PRINT 'Subject: [' + @emailSubj + ']'
END