An error occurred while signing

I'd check whether the certificate expired. Most (all?) certs have an expiration date.

Go to main project properties > Signing > If the expiration date is over > click on Create Test Certificate, password is not mandatory, and you're done.

I got this problem installing visual c++ on top of a VS2017 .net install. I solved it by unchecking Properties -> Security -> Enable ClickOnce security settings.

It then created an app.manifest file. After that the error went away. Interestingly enough, I checked it again to see what would happen and the problem did not come back.