It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level.

If you see this problem using ASP.Net Publish then try:

  del "$(ProjectDir)\obj\Debug\Package\PackageTmp\web.config"

from: http://stackoverflow.com/questions/2147180/why-do-i-randomly-get-a-error-to-use-section-registered-as-allowdefinition-mach

Wasted ages on this... gggggggggrrrrrrrrr!