The backend.dll file is a component of 1C:Enterprise 8.1, an accounting system made by the Russian software giant, 1C. 1C is known in Russia for 1C:Enterprise, a business solutions package used by thousands of companies. It is better known in the West for video games, including simulation games. And while backend.dll is part of the business software, dynamic link libraries are designed to share code among multiple programs. There is a tiny chance that if you have a 1C game on your system, this dll might be a part of it.
If this file is moved or overwritten you might get an error message listing the file. At that point, you will need to either locate the file and fix the registry (not recommended!) or move the file to the place where it needs to be. Of course, it can be slightly difficult to figure out where the file should be placed.
To make it easy, run a registry cleaner. ZookaWare PC Cleaner will do the work for you, and get your computer back up and running again without strange errors.