Web.config Attribute Not Being Updated.

I have a web.config that looks like this: 

<?xml version="1.0"?><configuration><appSettings><add key="fileLoggerMaxFileAgeInDays" value="" /></appSettings></configuration>

My parameters file looks like this: 

<?xml version="1.0" encoding="utf-8" ?><parameters><parameter name="fileLoggerMaxFileAgeInDays" defaultValue="10"><parameterEntry kind="XmlFile" scope="web\.config$" match="/configuration/appSettings/add[@key='fileLoggerMaxFileAgeInDays']/value/text()" /></parameter></parameters>

However when I try to update the attribute value in the web.config by importing through IIS I get the following error message: 

Parameter entry 'fileLoggerMaxFileAgeInDays/1' could not be applied to 'Web.Config'. Deployment will continue with the original data. Details:
No matches were found for the search string '/configuration/appSettings/add[@key='fileLoggerMaxFileAgeInDays']/value/text()' (type 'XmlFile').

Anyone have ideas why this isn't working? The XPath above seems to be the recommended way to update web.config appsettings but isn't working for me.