Dealing With Datetime And SQL Transact-SQL

I am trying to make a stored procedure in SQLServer Express.
The question is related to this stored procedure / transact - sql.
 I think i am doing something wrong with datetime.
Here is the stored procedure.
The error i am getting is that:
Msg 241, Level 16, State 1, Line 20
Syntax error converting datetime from character string.

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DECLARE    @websiteID  int
DECLARE    @dateFrom  datetime
DECLARE    @dateTo  datetime
DECLARE    @sortbystring  varchar (20)

set @websiteID = 1
set @dateFrom = Convert(datetime, '2007-02-07 12:01:00')
set @dateTo  = Convert(datetime, '2007-03-07 11:59:00')
set @sortbystring = 'Campaign'

IF ISNULL(@dateTo, '') = ''
begin
    SET @dateTo = @dateFrom
end

SET @dateTo = DATEADD(d, 1, @dateTo)

DECLARE @str CHAR(400)

LINE 20: SET @str = 'SELECT dateEntry, c.name as Campaign, e.firstname as FirstName FROM entry e, campaign c WHERE e.campaignID = c.id ' + 'AND c.websiteID = @websiteID' + 'AND (ISNULL(' + @dateFrom + ', '''') = '''' OR e.dateEntry BETWEEN '' + @dateFrom + '' AND '' + @dateTo + '') ' + 'AND e.IP NOT IN (SELECT IP FROM IP) ' + ' ORDER BY dateEntry DESC'
print (@str)


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