CONTROL_FLUSH_ERROR when using 'GUI_DOWNLOAD' Function Module in foreground

Hello,

I am using function module 'GUI_DOWNLOAD' in foreground mode with APPEND = 'X' ( I need to add Header details to file ).

In most of the cases it works good but in some cases ( which I cannot isolate ) - I am getting CONTROL_FLUSH_ERROR exception. Do you have any ideas where can be the problem?

Thanks,

Balu B