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That error message strikes me as very strange. What business does the Extension have trying to convert

VSTSAccountName

to an int? That should always be a string

Hello Willem, Yes my thoughts exactly. I've managed to create and run a powershell script and this method works. The stranger part to the c# class above is, if I don't pass any values { } in the settings parameter it still complains with the same error message. I think there might be a bug in the VirtualMachineExtension.