VPN At Windows 2000

I am using windows 98 vpn client to connect to a VPN server. The windows 98 is using dial up to the internet. On the second connection using the vpn adapter, there is an error “The microsoft dial up adapter is in use or not responding properly. Disconnect other connections anf then try again’. Click ok will show the next error ‘You have been disconnected from the comoputer you dialed’

Can I know how to fix the problem. I have installed dun 4 but still cannot work

Thank you