Hi Keshav,
Going by all the inputs, it seems out to be a case where I am certainly missing out something but couldn't find out due to non availability of system.
In this case, the best and time tested way out at last will be to debug the behavior at the Feeder system itself when the invoice is saved. This will certainly give you an idea about why the document is not getting generated at the GTS end. In case of further help, please feel free to ask me again.
Regards,
Aman