IE 8 is rather fickle. You can try to force IE-7 compatibility mode. In our latest version we have that turned on by default. In your version, you'd need to actually add it. The post below has the line that needs to be added and where it needs to go.
https://www.ubbcentral.com/forums/u.../Re_Cant_login_with_IE_8.html#Post226676
