no imovie export at all works

I finished an iMovie project on my iPhone 5s (iOS 9.2). I tried to export it in any possible way - no chance. I cannot safe it on my iCloud-drive, I cannot save it as a Video on my phone, I cannot save it in my dropbox, not upload it to YouTube etc.

I just get recent error-messages after the export is done. I restarted my phone. Deleted several files to free more storage space. I have no more idea what to do.

Anyone?