Problem 1: i'm suspecting that the .NET Framework
version with which you built the Application is heigher than what client is using.
Solution 1: try to build your appliction with the client compatible .NET Framework
version.
Problem 2: You might be building your application with X64
option in build settings.
Solution 2: change the Platform Target
of the Application from X64
to X86
from buid settings and rebuild your application.