Why can't I read from a file in Entity Generation's Intergeneration Time Action?

The Code:

persistent rngInit;
coder.extrinsic('str2num');
coder.extrinsic('fgetl');
if isempty(rngInit)
    SeedfileID = fopen('Seed.txt');
    SeedString=fgetl(SeedfileID);
    fclose(SeedfileID);
    Seed=str2num(SeedString);
    Seed=uint16(Seed);
    rng(Seed);
    rngInit=true;
end

mu = 12;
dt = -mu * log(1-rand());

Problem is that Seed always comes back as 0. The input file contains a single line of text containing "6<newline>" (without the quotes)