So, I solved the problem myself after a long time. And I am writing here how I solved the problem for possible needs in the future.
The reason I was getting the error "Error: could find generator in Cache" after typing "cfg = configureSim();BuildSimulation(cfg);" is CMake had used "Visual Studio 10" instead of "Visual Studio 10 Win64" as generator while trying to build the source code from directory "C:/spheres/trunk/MatlabSim/CSPHERESCore/SimVerification" to directory "C:/spheres/trunk/MatlabSim/CSPHERESCore/SimVerification/build". Therefore the "build" file was empty and I was getting that error.
After changing generator from "Visual Studio 10" to "Visual Studio 10 Win64" and configuring again, required files were generated in "build" file. After that I successfully finished installing the SPHERES Simulation. Here, I am writing step by step how I solved the problem.
(i) From start menu I clicked on CMake (cmake-gui)
(ii) On that gui, I clicked on the "Browse Source" button and chose "C:/spheres/trunk/MatlabSim/CSPHERESCore/SimVerification"
(iii) Then I clicked on the "Browse Build" button and chose "C:/spheres/trunk/MatlabSim/CSPHERESCore/SimVerification/build"
(iv) After that, I arranged generator as "Visual Studio 10 Win64" instead of "Visual Studio 10"
(v) Finally I pressed the button "Configure".
Then I went back to Matlab and followed the remaining steps and installed the SPHERES Simulation.