I’m having the same problem – the sharepoint assigned a CNAME record for the “companyweb some how it is not been registered at the DNS zone. I have tried changing the type of record, security access, created new virtual folder and nothing has worked for me, except by adding the host name at the client computer. If you go under C:/windows/system32/drivers/ect you will see a file call "hosts" that you will be able to edit with notepad by adding the IP address of the server and domain name at the end of the file (192.168.X.X companyweb) – once saved you should be able to reach the site; however that is not the best way to do it. I really don’t know much about CNAME and child site – but the problem is right there.
hope some has a better or the right solution
ASD