The problem is that there is no function named FluxSmooth (coincidentally, this is exactly what the error message tells you). The filename FluxSmooth.dll is slightly misleading in this regard; the actual function names that are available, as specified in the
readme, are FluxSmoothT and FluxSmoothST. The former only provides temporal smoothing, the latter provides both spatial and temporal smoothing.
I should note that there's no need to load filters that are already in your plugins directory, so your third line is redundant.