Error when using cast and convert to datetime

Question

I run a stored procedure
usp_ABC
as
begin
delete from #temp1 
where #temp1.ResID not in 
( select Col1 
from TableA 
where ( @I_vId = -1 or Doc_Field_ID = @I_vId)
and ColA1 = 2  and FieldValue !=''
and cast ( FieldValue as DATETIME ) = cast (@strvalue_index as DATETIME)
and ResID = #temp1.ResID
and TypesId = @I_vTypeId
end
But return message "Conversion failed when converting date and/or time from character string.'
Format of Column FieldValue is nvarchar(400)
@strvalue_index = '05/05/2013'
So I see in article http://technet.microsoft.com/en-us/library/ms174450.aspx MS say about MS SQL Server and SQL Server Compact.
Then I re-write proc:
delete from #temp1 
where #temp1.ResID not in 
( select Col1 
from TableA 
where ( @I_vId = -1 or Doc_Field_ID = @I_vId)
and ColA1 = 2  and FieldValue !=''
and cast ( cast(FieldValue as nvarchar(200)) as DATETIME ) = cast (@strvalue_index as DATETIME)
and ResID = #temp1.ResID
and TypesId = @I_vTypeId
so stored run success.
I don't understand how?
When i run only statement in MS SQL Studio Management, the statement run success.
Thanks all,

Answer 1

No bad dates in my data.
Apparently you have. Or, as Johnny Bell pointed out, there is a clash with date formats. Did you try the query with isdate()?
For SQL 2008, you need
  CASE WHEN isdate(FieldValue) = 1
       THEN CAST (FieldValue AS datetime)
  END =
  CASE WHEN isdate(@strvalue_index) = 1
       THEN CAST (@strvalue_index AS datetime)
  END
Erland Sommarskog, SQL Server MVP, [email protected]
I think date formats is OK. So when I re-write stored:
and cast ( FieldValue as DATETIME ) = cast (@strvalue_index as DATETIME)
=>
and cast ( cast(FieldValue as varchar(200)) as DATETIME ) = cast (@strvalue_index as DATETIME)
the stored procedure will run success. I see in http://technet.microsoft.com/en-us/library/ms174450.aspx MS
has an IMPORTANT:
 Important
When using CAST or CONVERT for nchar, nvarchar, binary, and varbinary,
SQL Server truncates values to maximum of 30 characters. SQL Server Compact allows 4000 for nchar and nvarchar, and 8000 for binary and varbinary. Due
to this, results generated by querying SQL Server and SQL Server Compact are different. In cases where the size of the data types is specified such as nchar(200), nvarchar(200), binary(400), varbinary(400), the results are consistent across SQL Server and
SQL Server Compact.
I can't explain it in this case