There's a variety of reasons why this could be happening.
1) .NET framework isn't installed correctly or the version you developed the application does not match the end machine .NET version.
2) DevExpress puts the assemblies on your Global Assembly Cache. The application running on the end machine must a way to find these assemblies.
In this case you have 2 choices:
- Place the DevExpress DLLs you are referencing in the same directory the application is running (recommended)
- Install DevExpress / Copy the DLLs to GAC on the end machine