When deploying CUDA add-ins to a machine other than the development machine, you must ensure that the appropriate CUDA run-time DLLs are also present. These include cudart*.dll and optionally curand*.dll, cufft*.dll, cusparse*.dll and cublas*.dll.
It is not enough to deliver these to the directory that contains the XLL add-in. They need to be delivered either to a directory on the machine's PATH or to the directory that contains EXCEL.EXE.