Programmatically installing plugins from Eclipse plugin: error processing mirrors URL - eclipse

Question

In our project (an Eclipse plugin), we're trying to install a couple of plugins programmatically (no worries, the user first has to accept all their licenses). Everything works fine, the plugins get installed, except that a certain error keeps popping up:
eclipse.buildId=M20120208-0800
java.version=1.6.0_43
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=nl_BE
Framework arguments: -product org.eclipse.epp.package.rcp.product
command-line arguments: -os win32 -ws win32 -arch x86_64 -product
org.eclipse.epp.package.rcp.product
Error
Thu Nov 07 12:32:22 CET 2013
Error processing mirrors URL:
http://www.eclipse.org/modeling/updates/countryCode=be&timeZone=1&format=xml
java.io.FileNotFoundException:
http://www.eclipse.org/modeling/updates/countryCode=be&timeZone=1&format=xml
at org.eclipse.equinox.internal.p2.transport.ecf.RepositoryStatusHelper.checkFileNotFound(RepositoryStatusHelper.java:297)
at org.eclipse.equinox.internal.p2.transport.ecf.FileReader.checkException(FileReader.java:384)
at org.eclipse.equinox.internal.p2.transport.ecf.FileReader.sendRetrieveRequest(FileReader.java:358)
at org.eclipse.equinox.internal.p2.transport.ecf.FileReader.read(FileReader.java:213)
at org.eclipse.equinox.internal.p2.transport.ecf.RepositoryTransport.stream(RepositoryTransport.java:153)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorSelector.computeMirrors(MirrorSelector.java:274)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorSelector.initMirrors(MirrorSelector.java:336)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorSelector.selectMirror(MirrorSelector.java:406)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorSelector.getMirrorLocation(MirrorSelector.java:314)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getMirror(SimpleArtifactRepository.java:651)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.downloadArtifact(SimpleArtifactRepository.java:568)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getArtifact(SimpleArtifactRepository.java:680)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorRequest.getArtifact(MirrorRequest.java:260)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorRequest.transferSingle(MirrorRequest.java:235)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorRequest.transfer(MirrorRequest.java:191)
at org.eclipse.equinox.internal.p2.artifact.repository.MirrorRequest.perform(MirrorRequest.java:122)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.SimpleArtifactRepository.getArtifact(SimpleArtifactRepository.java:664)
at org.eclipse.equinox.internal.p2.artifact.repository.simple.DownloadJob.run(DownloadJob.java:63)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)
We've tried a couple of things, like setting in the pom.xml for tycho that we don't want to use mirrors, or giving it as a JVM argument, or simply setting the System property to not use mirrors. However, as far as I understood, this will only cancel out non-eclipse.org sites and this is an eclipse.org site...
The updatesite to install from is: http://download.eclipse.org/modeling/emf/teneo/updates/2.0.0/interim/ (for Teneo).
What can I do to prevent this error from happening? To be clear: this doesn't prevent the code from running as it should. Teneo gets installed. I just don't want this kind of errors popping up in the Error Log.
Thanks for any tips.