Change your
File.Copy(DLLFilesForDir, Path.Combine(SADIR, DLLFilesForDir), true);
to
File.Copy(DLLFilesForDir, Path.Combine(SADIR, Path.GetFileName(DLLFilesForDir)), true);
From the MSDN page for Path.Combine():
If path2 contains an absolute path, this method returns path2.
So you are trying the copy the file onto itself ^^