Make sure Building Essentials isn’t running. The best way is to reboot your computer.
In your file manager (eg Windows Explorer) open the folder containing your bld files. Sort by NAME, you should see the bld with it’s filename preceded by a ~ and probably SIZE=1KB
Delete that file & it should be good to go.
Obviously if there are other bld files whose names start with ~ you can delete them as well (only when Envisioneer isn’t running).
hth
Merv