Share point names are case sensitive in Mac OS X 10.4 and later, meaning that "MyDisk" and "mydisk" will be seen as two different volumes, for example. If you enter the wrong name in the "Connect to Server" dialog, you might see this message:
Mount Failed
Could not mount volume "users."
If you make the same name mistake at the command line, you might see this error message:
mount_afp: the mount flags are 0000 the altflags are 0020 mount_afp: AFPMountURL returned error -5019, errno is 2
To avoid this issue, make sure that you are using the correct lettercase when entering share point or file sharing server names. If you're sure the name is correct as entered, it could be that the volume has become unavailable.