You have some problems with your quotes. I'm not sure that I did the right corrections. Use the print to run the query that gets printed and debug from it.

use webproxy

DECLARE @tempsql varchar(2000)

select @tempsql =

'declare @xmonth varchar(2)

declare @xyear varchar(4)

declare @xdate varchar(10)

declare @rptmonth datetime

select @xmonth = MONTH(dateadd(month,-1,getdate()))

select @xyear = YEAR(dateadd(month,-1,getdate()))

select @xdate = @xmonth + ''/01/'' + @xyear

select @rptmonth = cast(@xdate as datetime)

set rowcount 0

select dbo.user_parser(clientusername) as "_user",

count(*) as "objects",

sum(cast(bytessent as float))as "bytes_sent",

sum(cast(bytesrecvd as float))as "bytes_received",

(sum(cast(bytessent as float)) + sum(cast(bytesrecvd as float)))as "total_bytes",

@rptmonth as "rpt_month"

----into ##top100temp

from webproxylog''' + cast(month(dateadd(m,-2,getdate())) as varchar(2)) + '''

--from webproxylog5

where dbo.user_parser(clientusername) <> '' ''

group by dbo.user_parser(clientusername)

order by total_bytes desc'

--print @tempsql

execute (@tempsql)