Click the Sequences tab above the bin (top-left), then click on the sequence thumbnail. 
If there's no Sequences tab, click the + sign to the right of sequence 1 above the timeline to add a new blank sequence. 
Under the preview window, drag the red [ bracket to the far left and the blue ] bracket to the far right. There should be no shading on the thumbnails. Now try exporting. If that doesn't succeed, let's take a look, and it will quickly be solved...
Share your project. The process is easy, quick and can be done privately. Just follow these steps...
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.