Accesing Domain

Hello, can someone please help to find out why I cannot view the Domain. On my client, For example:
Right clicking on a Folder/File, then sharing, then ADD, it’s starts to search the exisitng Domain, but then it display Server unavailble. I can access the Domain thru My Network Icon on the desktop and access shared folders/files from the client. Is there a security setting or I am doing something wrong? Pls post msg if more info is needed.

Thanks in advance
KJG