Static IP address disappears from IP4 settings box

>I have the following problem with the "Use the following IP address:"
>setting in the IPv4 properties dialog box of my network card (under "manage
>network connections" in 32-bit Vista Ultimate):
>
> Everytime I enter my (local) static IP address, 192.168.0.124, and press
> OK, the address (and the subnet mask, 255.255.255.0) is blank when I
> re-enter the setup box. When I enter a different static IP address, such
> as 192.168.0.125, the problem does not occur.
>
> This may or may not be the effect of antivirus software I installed and
> then removed, but any suggestions as to how I should correct the problem?
> (To my knowledge this has not affected actual network operations, but
> perhaps it's a sign of a network stack corruption or security issue.)
>
> Thanks.
>