Broken pipe in rsync (but only in one direction...)

I've been using rsync to sync my Macbook Air and the iMac in my office.

It has always worked, until a couple of days ago.

Strangely, syncing from the Macbook to the iMac is no longer working.

Here's the error when I run the rsync command on my Macbook:

rsync -avz --update --exclude=.DS_Store --exclude="Microsoft User Data" ~/Documents/ myusername@mymachine.mydomain:Documents/

Password:

building file list ... done

Write failed: Broken pipe

rsync: connection unexpectedly closed (8 bytes received so far) [sender]

rsync error: unexplained error (code 255) at io.c(605) [sender=3.0.9]

In the reverse direction (i.e., exchanging the last two arguments of the above command) everything works flawless (like it always did).

I've tried rebooting both machines, as well as the Airport Time Capsule that connects the iMac to the internet (and eventually the Macbook via wifi, though the problem persists even if I connect the Macbook to any other network).

Any suggestions?