When an application is installed onto a computer using the "setup.exe" or similar method, not only is the application installed, but so are all of it's dependencies. Dependencies include all of the other libraries, user controls, and other such objects that are required by the application to run. If all of the applications' dependencies are not installed, then you may encounter an error as described when you attempt to run the application. For these reasons, you may not be able to execute an application simply by copying the "EXE" to your computer. It is best to actually install the application using the setup routines provided by the vendor. It is also possible to encounter this error if dependencies were accidently deleted from the computer, or were replaced by an incompatible version by another application.