Merge XML error

Hi,
I'm in a situation in which I have to generate two different report xml files, one from nunit tests, the other from mspec tests.
The report generation seems ok on both sides, but when I try to merge using the merge command I get the following output (in this case the mspec report file is the first one in the config):

JetBrains dotCover Console Runner v1.0.97.18. Copyright (c) 2009-2010 JetBrains s.r.o. All rights reserved. Failed to read source file 'D:/dev/myapp/trunk/src/bin/reports/dotcover-mspec-report.xml'. There is an error in XML document (2, 2).

If the nunit xml report file is listed first in the merge configuration file, the error is the same but the source file is the nunit xml report.

My merge configuration is the following:

<MergeParams>
  <Source> <!-- Required. At least one child element expected. -->
    <string>D:/dev/myapp/trunk/src/bin/reports/dotcover-mspec-report.xml</string>
    <string>D:/dev/myapp/trunk/src/bin/reports/dotcover-nunit-report.xml</string>
  </Source>
  <Output>D:/dev/myapp/trunk/src/bin/reports/dotcover-report.xml</Output>
</MergeParams>

If you need the coverage xml reports I can send them privately.