SQL Agent could not set a Value for a Date Time variable

Hi,

I'm trying to pass a Date as a parameter from SQL Server Job Agent (2008 R2) to an ETL.

 /SET "\Package.Variables[pPeriodoDesde].Value";"01/10/2012"

And when I try to execute it, I get the error: 

DTExec: Could not set \Package.Variables[pPeriodoDesde].Value value to '01/10/2012'. 

The variable in the ETL is a Date Time and package scope is set. I already tried to set the value without "" ( /SET "\Package.Variables[pPeriodoDesde].Value";01/10/2012) but I get the same error.

Any ideas?

Thank you!