The most likely answer is that the server computer does not support connections of the AppleTalk Filing Protocol (AFP) using the Transmission Control Protocol (TCP). That "Server IP Address" button only looks for server computers that use AFP over TCP.
Figure 2 Server IP Address Icon
This button is NOT for connecting to servers that have a TCP/IP address and provide some other service. Examples of servers that this button DOES NOT apply to include: Web (HTTP) Servers, Printer (LPR) Servers, File Transfer Protocol (FTP) servers, Network File System (NFS) servers, Windows (SMB) servers, and AppleTalk-only servers.
Examples of servers that can use AFP over TCP include AppleShare IP 5 and later and the Apple File Services built into Mac OS X Server. Third-party AppleShare servers may support this feature. Read the server documentation or contact the server manufacturer to find out for sure.
If you connect to one of the above servers, you will see a file server icon with a globe in the lower right hand corner of that icon.
Figure 3 AppleTalk Server Icon
Figure 4 TCP Server Icon
Also, the "Where" line of the info window will show you connected via AppleTalk or TCP/IP.
Figure 5 AppleTalk Connection
Figure 6 TCP Connection
Only versions 3.7 and later of the AppleShare extension (sometimes called AppleShare client or AppleShare workstation), will display this button.
You can find the current version of the AppleShare extension at the Apple Downloads Web site at
http://www.apple.com/downloads.