SourceForge.net recently updated its mirroring selection system. In the process, they introduced a bug that breaks every external link into a SourceForge download. I have a priority support request into them to fix it.
In the meantime, you can copy and past the link into a new tab/window for it to download. Just right-click on a download button or link and select Copy Link Location (IE user's: Copy Shortcut). Then open a new tab or window, right-click on the address bar and select Paste. Then click enter.
You can also use the SourceForge icon in the download details sections of the project pages to browse into the SourceForge project page and select a download from there.
I'll update as I learn anything.
Update (7:20pm NY Time): They've implemented a temporary fix (with a META refresh page).