Web Deployment Project - specify version of aspnet_merge to use

we are having some problems with our WDP, which is deploying a ASP.NET 4.0 site. It seems to all go fine but when its deployed we are getting the System.BadImageFormatException: Bad binary signature. (Exception from HRESULT: 0x80131192) error, when hitting a particular page , which appears - from other reading - may be to do with the version of aspnet_merge the WDP is using by default. thing is, we have just had all our machines changed and it was working fine on the old ones..

I have found how to specify which version in the Microsoft.WebDeployments.Targets file (enter link description here), but not convinced it is actually using that..

  <AspnetMergeName>aspnet_merge.exe</AspnetMergeName>
    <!-- OLD 
    <AspnetMergePath>$(MSBuildExtensionsPath)\Microsoft\WebDeployment\v10.0</AspnetMergePath>
    <AspnetMergePath Condition="Exists('$(TargetFrameworkSDKDirectoryBin)$(AspnetMergeName)')">$(TargetFrameworkSDKDirectoryBin)</AspnetMergePath>
    -->
    <AspnetMergePath>C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools</AspnetMergePath>
    <AspnetMergePath Condition="'$(TargetFrameworkVersion)' == 'v4.0'">C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools</AspnetMergePath>

I got the paths from here: http://msdn.microsoft.com/en-US/library/bb397866.aspx#findingthecorrectversion is there a way of setting the path to aspnet_merge directly in the wdproj file?

this is all assuming that this is the problem in the first place of course..

thanks

nat