ITS - upload/download of files - getting java error on download

Hi, I'm working on ITS to upload/download some files, really simple files in ASC and i use cl_gui_frontend_services=>gui_upload it works fine, and to download the cl_gui_frontend_services=>gui_download that in R/3 works but on the ITS give an error.

Any idea or someone that happend the same?

Thanks in advance to all

Regards

Jaime