Every now and then you may come across a video/audio that you can't import into WMM. You may get an Error message like: Cannot import media due to DMR,or File not classified, etc.
If you are unable to import a file it may be because you are trying to import audio or video that has been protected with digital rights management (DRM).
DRM is a technology that lets content authors and publishers, such as record companies and movie studios, control how their digital music and video files are used and distributed. Protected digital media files cannot be imported into Windows Movie Maker.
As such, you will have to find similar media without DRM encoded.
At times you may also find it difficult to import files because they are not supported by WMM. Some audio and video file formats are not supported in Windows Movie Maker and cannot be imported. However, if you have a video or audio file that is not supported, you may be able to use a non-Microsoft video editing program to convert the file into a format that Windows Movie Maker supports, and then import the resulting audio or video file into Windows Movie Maker.
Again, this is where your free video converter comes in handy. Make sure you are converting the file to a format used by WMM if that is where you intend to import the media.
Some people might suggest you download a codec (or codec pack) instead of converting the media with a video converter. I strongly advise against downloading codecs for this reason:
Codecs that you find on the Internet, particularly some of the free codec packs that claim to include codecs from a wide variety of companies or organizations: incompatibilities are known to exist with some of the components in these codec packs that can cause serious playback issues in the Player and other players, lead to system corruption and make it difficult for Microsoft Support to diagnose and troubleshoot playback issues. For these reasons, you are strongly discouraged from installing these codec packs, and recommend that you remove them if you have installed them and you are having problems with the Player. Install only codecs, filters, or plug-ins from trusted, authorized sources, such as the website of the official supplier. Even then, use caution; many codec suppliers offer minimal customer support. Before installing any digital media components, set a system restore point. The restore point enables you to return to your original system configuration, if necessary.
Personally, I have never downloaded any additional codecs(codec packs), filters or plug-ins to use my Windows Movie Maker or Windows Media Player. If I am unable to play a file, or import it into WMM, I simply convert it. Better safe than sorry.