I compiled 3.0.4 in OS X on an Intel machine. The resulting binary works on many other Intel Macs, but I've come across some 1.83GHz Core 2 Duo iMacs that won't run rsync. Here is the Terminal dump when simply trying to confirm rsync version.
[ ~/.bin ]$ /Users/admin/.bin/rsync-304 --version
dyld: Library not loaded: /usr/lib/libiconv.2.dylib
Referenced from: /Users/admin/.bin/rsync-304
Reason: Incompatible library version: rsync-304 requires version 7.0.0 or later, but libiconv.2.dylib provides version 5.0.0
You need to recompile rsync on one of the machines with the older libiconv. It's typical that a program compiled against one version of a shared library won't run with older versions of the library.
OK, this can be marked FIXED. I downloaded xCode on that iMac, recompiled rsync, and it works fine now!
Reopen to change resolution.
This was not a bug in rsync.