Why can’t I assign an IP address using a static entry in the ARP cache?

Why can’t I assign an IP address using a static entry in the ARP cache?

This method can only be used if the Web Thermometer does not already have a different IP address. (See also How can a Web Thermometer having an unknown IP address be assigned a new one?).
Some older Windows versions have a defective version of the program arp.exe, which is needed to edit the system-internal ARP cache. Here you can only make a new static entry if at least one other entry already exists. In this case, one remedy is to send a PING request to another TCP/IP station in the network, since this will force a dynamic ARP entry. The desired static entry can then be made immediately following.

Additional information: