Error parsing web.config file

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When I specify an end tag for the clear element of namespaces in my
web.config file, the parser error "Unrecogniz ed element 'add'" is reported.

....
<pages>
<namespaces>
<clear></clear>
<add namespace="Syst em"/>
....

When the same element is specified using the empty element tag syntax, it
works.

....
<pages>
<namespaces>
<clear/>
<add namespace="Syst em"/>
....

InstallSheidl/MSI is creating the XML file, and I therefore have no control
over the format details. Is this a known problem? How can I work around it,
short of generating the XML file myself?

Thanks