Problem completing download of flv files with IDM Internet Download Manager

Hi, I am trying to download .flv videos using IDM. It used to work before, but now the "download complete" dialogue doesn't pop up at the end of the process, even though it appears it has gotten to the very end of the file. The status remains "unknown" instead of "complete". I don't want to make any changes to my system or download any other software to succeed, unless I really have to. I'd rather just figure out what has changed. I tried it on my other computer, and it has the same problem. One video downloaded successfully, but that was one out of 4. My newest computer is a win 8, and the other is win 7(this one was successful, and the system had a recent clean install of the operating system). Please help. I paid good money for the videos, and they are taking them down/changing them, and I don't have much time. If I was successful before, I don't understand what the problem could be. The IDM people are very inaccessible. You can't call them, have to fill a form for support, which doesn't confirm that your request has been receive. Please help. Thanks in advance.