Hello,
If you're just transferring the .MSWMM (Windows Movie Maker Project) file to the other PC, and opening it with Windows Movie Maker, it won't work.
Quite rightly, it won't be able to locate the files necessary because you've not transferred the video / audio / image files along with the .MSWMM file.
The .MSWMM (Windows Movie Maker Project) file doesn't contain any media. It's a file which contains references to the media files which make up the project.
So, if you want to be able to edit the project using Windows Movie Maker on another PC, you need to transfer both the .MSWMM file and the media files. Not only this, but the media files need to be in the exact same directory structure as they were on the originating PC. That is, if a video file was imported from C:\Videos\ to Windows Movie Maker on the originating PC, for example, then when you transfer the project file and media files to the new PC, the video will also need to be in the location C:\Videos\ on the new PC. Otherwise, Movie Maker won't be able to locate the files because the references are no longer valid.
If you simply want to
watch the video on another PC,
and not edit the project on another PC, then you are supposed to publish the project by going to File > Publish Movie... in Windows Movie Maker. Movie Maker will then create a single .WMV video files of all media objects in the timeline. You can then transfer and watch the .WMV file on another PC.