I tried to add Cloud Service (classic) to Virtual Network (classic), but an error appears when I deploy (new portal - Update your deployment):
The update deployment operation failed for the domain 'developementtajgowebservicev1' in the deployment slot 'staging' with the name 'not working': 'The virtual network devvirtual-Network does not exist.'.
I added this code after Role tag into config file.
<NetworkConfiguration>
<VirtualNetworkSite name="devvirtual-Network"/>
<AddressAssignments>
<InstanceAddress roleName="WorkerRole1">
<Subnets>
<Subnet name="Subnet-1"/>
</Subnets>
</InstanceAddress>
</AddressAssignments>
</NetworkConfiguration>
The virtual network with this name exist in same subscription.