1. In your browser, click on "Tools" and select "Internet Options".
   
2. At "Privacy", click on "Advanced"
   
3. Make sure you accept cookies and put a check mark on "Always allow session cookies" and click "OK".
   
4. Restart the browser and try to sign in again.

If you are using IE 5.5 or below, do the following steps:

1. In your browser, click on "Tools" and select "Internet Options".
   
2. At "Security", select "Internet" and click on "Custom level".
   
3. Find "Cookies" in "Settings" selection box.
   
4. Make sure to select "Enable" on "Allow cookies that are stored on your computer"and on "Allow per-session cookies (not stored)" and click "OK".
   
5. Restart the browser and try to sign in again.