IE9 Beta causes SEP client not to update virus definitions and sometimes in windows 2008 R2 servers have got installed IE 9 beta
Follow the below steps
1.Go to Programs and Features -- Turn Windows Features on or off --then click on view updates
2. In the list of installed updates, double-click Windows Internet Explorer 9.
3. In the Uninstall an update dialog box, click Yes.
Note If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
4. Follow the instructions to uninstall Internet Explorer 9.
5. When the uninstall program is finished, restart your computer.
6. If you have IE 8 downloaded then install it and check it.