The root cause of this issue was bad entries in the web.config file located in the same directory as the GetResourceGuid.aspx ../Altiris/Deployment/Agent/web.config However it is still uncertain how the web.config gets bad entries in it.
Replace the web.config file with a known good copy from a working environment. If you do not have access to a known good web.config file there is one attached to the document.
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