Boot up time problem

Has anyone ever seen this message before? When I try to change the NT4 Boot-up time from the default 30 secs to my usual 5 secs, I get this pop-up message in a “System Control Panel Applet” box:

“The C:\boot.ini file can not be opened. Operating System and Timeout settings can not be changed”

I have tried to do the change as Administrator and as the user. Any help would be much appreciated…