RHN XML-RPC system.setChildChannels issue

I'm trying to use the RHN XML-RPC API (yes, that was 4 TLAs in a row)
to automatically subscribe my systems to a set of channels. Here's the
request I send (with added whitespace for legibility) with Perl's
RPC::XML::Client:

<?xml version="1.0" encoding="us-ascii"?>
<methodCall>
<methodName>system.setChildChannels</methodName>
<params>
<param><value><string>3543551944xec1c4bd26c181f4f045f65b33d2f0cda</string></value></param>
<param><value><int>1234567890</int></value></param>
<param><value><array><data>
<value><int>6958</int></value>
<value><int>6962</int></value>
</data></array></value></param>
</params>
</methodCall>

(SystemID and session string have both been changed, but format
retained.)

The error I get back is:

unhandled internal exception: java.lang.Integer (-2)

I've looked over the API, and it's expecting three arguments of
string, int, and array type, respectively. The array appears to be an
array of ints, as far as I can tell.

At this point in the script, I've logged in and gotten a list of the
child channels, both of which requests work just dandy.

What am I doing wrong?

Chris St. Pierre
Unix Systems Administrator
Nebraska Wesleyan University