nant: invalid element nunit2. Unknown task or datatype

Question

How to solve this problem?

I have this ProjectName.UnitTests.config file, and I did exactly what the documentation said: http://nant.sourceforge.net/release/latest/help/tasks/nunit2.html

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
     <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            <dependentAssembly>
                <assemblyIdentity name="nunit.framework" publicKeyToken="96d09a1eb7f44a77" culture="Neutral" /> 
                <bindingRedirect oldVersion="2.0.6.0" newVersion="2.2.8.0" /> 
                <bindingRedirect oldVersion="2.1.4.0" newVersion="2.2.8.0" /> 
            </dependentAssembly>
        </assemblyBinding>
    </runtime>
</configuration>