IDM downloads just a part of a video (for example 1.99MB or 1.69MB) instead of the full video. Why can this happen?

When I click on a download panel, IDM tells that some unknown error occurred. Why can this happen?

This happens when you have installed some video accelerator to speed up loading of videos in web players. It can be some kind of Video acelerator for example. We added workarounds for problems with video accelerators in one of latest builds. This why make sure that you use the latest version of IDM. But even the latest version may have conflicts with some accelerators. We recommend you to uninstall such programs. If you use IDM to download videos, you already have maximum possible download speed.