Unable to make connection to Web Folders

Desktop OS = Windows XP Pro SP1
Network Servers = NT 4.0 SP6a
Internet connection = Permanent 512kb SDSL

When using the “Add network place” wizard to establish a Web Folder under My Network Places get message after the authentication window:
“the folder you entered does not appear to be valid. Please choose another folder”

When connecting to this web server via IE6.0 using the same PC (XP Pro) I can successfully authenticate and use the folder.

I have spoken to another user of this web folder service and he can connect successfully via this method using XP Pro.

Windows 95 & 98 users have no problem

Does anyone have a solution please