Problems with http call

Hi experts!

I'm doing a scenario step to create a XML files with a http call. My step works well but I'm trying to send parallel http calls for do faster my proccess and here is the trouble. When 2 http calls come in at the same time I get this exception

com.sap.b1i.xcellerator.XcelleratorException: XCE001 Nested exception:

com.sap.b1i.xcl_file.FileAdapterException: FIE001 basePath or pattern is 'null'

java.io.IOException: El sistema no puede encontrar la ruta especificada

My scenario step is this

I really need to send parallel calls but I don't know how control this. Could anyone help me?

Does anyone know if it exists a way to solve this?

I hope somebody can help me.

Kind regards,

Samuel