The cause of this problem is probably that there is no matching between the video frame&format that you have defined in the Config Editor ("Format" field in the "Video" tab) and the clip that you are trying to import.

The video's format and the fps of the clip should match, if not, you won’t be able to import the video into Coach Paint.

But there is a workaround for this problem.

To avoid having to match every single video format, you can just import clips into Coach Paint with this option unmarked:

The option “Match Video Format” enabled will allow you to import only videos with the same format & frequency; while having it unmarked will allow you to import any format video. Importing any type of format or frequency could probably affect the quality of the video but it is way simpler and faster than trying to match every format.

But, even if you are not working with this option enabled, you should select a format and frame from the Config Editor, as every video that you are going to export from Coach Paint, will have those values.

Learn more in "Exported videos are reproducing faster or slower".

This option is convenient If you rather working with just one type of video format and frame, just follow these steps to configure the format and the frame rate of your clips:

Note: bear in mind that you will have configured Coach Paint to work with those video rates and formats. Work with the “Match Video Format” enabled and import clips of those rates only. If you need to import another format or rated video, export the existing videos and follow the same steps in order to configure it correctly.

If the format that you need is not appearing in the standard options, you may need to render your clip, so you can transform it into one of those formats (or disable the Match Video Format option).