I could not be heard by ISS

Greetings ISS Fan Club, I decoded some packets from the ISS ok today, but was unable to be heard by them, I dont understand why this was so.

I received this solitary packet from the ISS.
Orbit 29104 over sth eastern Australia.
Local time was 26-12-2003 7.04 pm
*********************************************************
Fm RS0ISS-4 To VK5DG-3 [19:04:08]
*********************************************************

and then this on orbit 29108
Local time was 27-12-2003 1.26-1.32 pm
*********************************************************
Fm RS0ISS-4 To CQ Via SGATE [01:26:33]
>ARISS - International Space Station (BBS/APRS on)

Fm RS0ISS-4 To CQ Via SGATE [01:30:33]
>ARISS - International Space Station (BBS/APRS on)

Fm RS0ISS-4 To CQ Via SGATE [01:32:33]
>ARISS - International Space Station (BBS/APRS on)
*********************************************************
I tried to digipeat but seemed to be unable to despite using the calls
ARISS, RS0ISS, RS0ISS-1, RS0ISS-4.
I transmitted on 145.990 MHz and received on 145.800 MHz. I am at a complete loss as to why I was not digipeated, any suggestions anyone?

OK, I read thro