Currency Exchanges rate values return -1 instead of orginal values using ssis webservice task

Hi ,I have doubt in ssis,

get usd to gbp  exchange rates conversation information for daily basis

here I Done current live values for ssis package ran day information values using webservice task.

 get currency
 exchange rates  for  USD to GBP.
 to run ssis ETL package daily,pull the data from webservice on the web and insert into the stage table.
step 1 : open new project of integration services and rename the default package name as webservice
step 2 : drag and drop the webservic task in package and  a variables (GBP_value)
step3 : create new HTTP connection by right clink in connnection manager and select http connection and enter the server url as
 http://www.webservicex.net/CurrencyConvertor.asmx?WSDL and testthe test connection.
step 4: open the new notepad and save it as currencyconvertor.wsdlfor required location .
step 5 : Double click on the web service task and confiure like belowin 
general tab: Httpconnection .....>http connection manager which we create earlywsdl file .....> browse and select the currencyconvertor.wsdl 
fileoverwritewsdlfile.....> set as truedownload the wsl file and overwrite to empty wsdl fileinput tab:in input tab 
we have to configurservice .....>currecconvertormethod.....>convesionrateand also 
I need to select the from currency value and tocurrencyvalueFromCurrency as usd(us dollar) 
and Tocurrency(GBP uk)output:in output tab i have to configur the output type : variable : GBP_value

step 6 : from the datafow to insert the stagein oledb source select data access mode : sql command

select getdate()as daterun ,convert(nvarchar(4000),NULL)as viewxml ,convert(nvarchar(3),'GBP')as currencytype

then fields list like daterun,viewxml,currencytypederievd column to expression : @[user::GBP_value]insert to stage dimcurrencystage.
after that take another dft and drag and drop oledb source and dataaccess is sql command and write query like 

SELECT [Currencytype] = [CurrencyAbbr] [DateSK] = convert(int,convert(varchar(8),Convert(date,[DateRun]),112)) 
,[ExchangeRate] = CONVERT(Decimal(18,2),CAST(CAST(ViewXML AS XML).query('data(/double)') AS varchar(4000))) FROM
[dbo].[DimCurrency_Stage]

then this data load in to final table.its working fine some times.but 

when I ran websrvice package some time its returning -1 as usd to GBP conversion.

can you please tell  me why its returning -1 instead of orginal values.

when -1 values return how to handle that case .please tell me how to achive this task in ssis.