You set Host pipe. It means you need to fill pipe name like this: \.\pipe\VirtualMachineName
Moreover, as Robin Hood mentioned you need to uncheck Connect to existing pipe/socket it helps don't create a pipe manually. After launch Virtual machine you can check created pipe via pipelist application. You should see VirtualMachineName on the list.
pipe_returnb2848f45-49cf-444b-85a1-04af7fe5606e 1 128
mojo.9004.8732.10216662671524970515 1 1
mojo.9004.9560.12163195199288806074 1 1
mojo.9004.9560.2084235546261883787 1 1
VirtualMachineName 1 1
You can read what is pipe here. A pipe isn't a simple file.