from your post in printf() topic i assume that you have instaled GeForce 275 with OpenCL enabled driver. so when you run opencl sample from ati stream sdk it use nvidia OpenCL library. so on linux you must export LD_LIBRARY_PATH to OpenCL library from stream sdk. you run
export LD_LIBRARY_PATH=/path/to/ati-stream-sdk/lib/x86_64
then it should load libOpenCL.so from ati sdk folder. you can confirm which lib is loaded with ldd command. "ldd name_of_executable" it print out every dynamic library whis is loaded at start.