I'm literally tearing my hair out to try and understand this problem
so any help would be greatly appreciated

I have Rsync 2.5.6 on two fairly new Sparc systems running Solaris 9

$ uname -a
SunOS neptune.xyz.net 5.9 Generic_112233-08 sun4u sparc

$ uname -a
SunOS saturn.xyz.net 5.9 Generic_112233-08 sun4u sparc

When I try and sync a filesystem between them, I get the following:

$ rsync -avvvv -e ssh /opt/abc/test test@saturn:/opt/abc/test

cmd=ssh machine=saturn user=test path=/opt/abc/test/
cmd=ssh saturn -l test rsync --server -vvvvlogDtpr . /opt/abc/test/
opening connection using ssh saturn -l test rsync --server
-vvvvlogDtpr . /opt/abc/test

After displaying the motd and asking for the "test" user's password, I

rsync: connection unexpectedly closed (0 bytes read so far)
_exit_cleanup(code=12, file=io.c, line=165): entered
rsync error: error in rsync protocol data stream (code 12) at
_exit_cleanup(code=12, file=io.c, line=165): about to call exit(12)

I have even turned on PortForwarding in SSH to see if that helps, but
to no avail. I have also tried doing this from saturn to neptune but I
still get the same errors.

Could someone please tell me what I'm doing wrong here?