I just did a model of spatial competition between two species with different competitive ability & dispersal rates on a lattice with variables nrs of individuals per site. To speed it up I tried to use Compile - but I get an error at runtime. It works OK though if I run it uncompiled. Anybody any ideas what I might be doing wrong? My code is

gridsize = 30;
k = 1000;
zeroMatrix[n_, m_] := Table[0, {n}, {m}];
initSpace[n_, m_, k_] := Block[{s},
   s = { zeroMatrix[n, m], zeroMatrix[n, m] };
   s[[1, 1, 1]] = k;
   s[[2, n, m]] = k;
   Return[s];
   ];
current = initSpace[gridsize, gridsize, k];

This function does one time step iteration, using synchronous updating:

stepC = Compile[{{current, _Real, 3}, {b, _Real, 1}, {disp, _Real, 
     1}, {fitness, _Real, 1}},
    Block[{tmp, k, k2, n, m, curr = current},
    n = Dimensions[curr][[2]];
    m = Dimensions[curr][[3]];
    Do[
     curr[[species]] *= b[[species]];
     curr[[species]] += 
      Map[Round, 
       GaussianFilter[curr[[species]], disp[[species]]], {2}];
     , {species, 2}];
    tmp = (fitness[[1]]*curr[[1]] + fitness[[2]]*curr[[2]]);
    k = Max[curr];
    Do[
     k2 = If[tmp[[i, j]] < k, tmp[[i, j]], k];
     tmp[[i, j]] = If[ tmp[[i, j]] == 0, 1, tmp[[i, j]] ];
     curr[[1, i, j]] = k2*fitness[[1]]*curr[[1, i, j]] / tmp [[i, j]];
     curr[[2, i, j]] = k2*fitness[[2]]*curr[[2, i, j]] / tmp [[i, j]];
     , {j, m}, {i, n}];
    curr
    ],
   CompilationTarget -> "C", Parallelization -> True, 
   RuntimeOptions -> "Speed"];

I then define a function to display the densities of the two species:

getImage[current_] := Module[{img},
   img = Map[{#/k, 0, 0} &, current[[1]], {2} ];
   img += Map[{0, 0, #/k} &, current[[2]], {2} ];
   Return[Graphics[Raster[img]]];
   ];

And iterate and display an animation of the dynamics:

b = {2.0, 2.0};
d = {3.0, 1.0};
f = {1.0, 1.3};
current = initSpace[gridsize, gridsize, k];
ngens = 30;
steps = 5;
imgs = Table[0, {ngens}];
Timing[Do[
  imgs[[i]] = getImage[current];
  Do[current = stepC[current, b, d, f], {steps}];
  , {i, ngens}]]
Animate[
 imgs[[i]]
 , {i, 1, ngens, 1}, AnimationRepetitions -> 1, 
 AnimationRunning -> False]

During runtime I then get an error "CompiledFunction::cfne: Numerical error encountered; proceeding with uncompiled evaluation." Any thoughts what's wrong?