Forum posts not shown in Homepage

I have the Forum Post block in my homepage, but no post is shown. I search for this issue in this Forum and found many people has the same problem, but I didn't find a solution for that.

Does anybody know how to fix this issue?

check the rss feed into it?

I have not changed the rss feed. It's the default one:

{SiteUrl}forum/?action=rss_all

Any suggestion?

I just managed how to solve this issue. And guess what... I just moved from IE to Firefox. Or Chrome, or Safari.

And now, can anyone help me to solve this issue for IE 9?