joinsysdef wasn't properly translating the namespace prefix for "replace".
<?xml version="1.0" encoding="ISO-8859-1"?>
<build xmlns="http://symbian.com/xml/build" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://symbian.com/xml/build ../../schema/build/2_0.xsd">
<!-- interfaces which do not correspond to target types:
they are added automatically to the build specification for a given
build configuration if listed in its INTERFACE.config variable -->
<interface name="Symbian.config.default" flm="config/default.flm">
<param name='EPOCROOT'/>
<param name='ELF2E32' default=''/>
<param name='WHATLOG' default=''/>
</interface>
</build>