Version 7.11 is dated. Suggest you update to the current release which you should be able to use unlicensed, with some limitations. If mp4 export doesn't succeed, use AVI. You might also test this version, which was released within the six-month free upgrade grace period and should accept your registration info. Normally, exporting with the same version or one close in time to the one that created the video is the best policy.
If no success, take a minute to share the project and someone here will come up with the fix. It's easy, quick, and can be private. Follow these steps closely...
Back up --- With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
Upload --- Use a free server - Google Drive, MS OneDrive, etc.* - to upload the saved, numbered FOLDER. Do NOT upload the individual VPJ or export file.
Get link --- Get a public link. If using Google Drive click GET SHAREABLE LINK. If necessary change "restricted" to "anyone with the link can view"
Share --- Click COPY LINK | DONE. Paste that link here, or click the folder at the top-right of this forum to message it privately to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.