
XML-RPC faults are a type of responses. If there was a problem in processing a XML-RPC request, the methodResponse element will contain a fault element instead of a params element. The fault element, like the params element, has only a single value that indicates something went wrong. A fault response might look like:
<?xml version="1.0"?>
<methodResponse>
<fault>
<value><string>No such method!</string></value>
</fault>
</methodResponse>
A fault will also have an error code. XML-RPC doesn't standardize error codes at all. You'll need to check the documentation for particular packages to see how they handle faults.
A fault response could also look like:
<?xml version="1.0"?>
<methodResponse>
<fault>
<value>
<struct>
<member>
<name>code</name>
<value><int>26</int></value>
</member>
<member>
<name>message</name>
<value><string>No such method!</string></value>
</member>
</struct>
</value>
</fault>
</methodResponse>