favicon works intermittently

I created an icon and placed favicon.ico in the main directory of the web
site. The html below is placed in the head of the code before the </head>.
<LINK REL="shortcut icon" href="http://www.mysite.com/favicon.ico"
type="image/x-icon">
At first, my favicon.ico was showing in the url and in the tab of IE7.

I logged in again a number of hours later and it is no longer working. Do I
need another line of code?

Thanks.