Accessing Client

hello, I have a question on why on my server when I try to access a client shared folder/files that I get a logon screen asking for username and password. Once I enter this info, all is fine and I can access view items from the client. From the client side when I access shared folders/files from the server, I have no problem viewing them. Is it my client computer thats causing this or is it the server?

Thanks in Advance.
KJG