Deleting a symbol

Maybe stupid question: how to delete a symbol allocated on the CUDA device ?

For example allocating:
device constant int Nx_device; …
cudaMemcpyToSymbol(Nx_device, &Nx, sizeof(Nx)); // works

But deleting doesn’t work :
void* devPtr;
cudaGetSymbolAddress(&devPtr, Nx_device);
cudaFree(devPtr);
It gives in VS 2005 debug mode an error:
“First-chance exception at 0x7c812aeb in CudaConsole.exe: Microsoft C++ exception: cudaError at memory location 0x0012f76c…”