Trouble using lsqcurvefit function to determine 2 unknowns

Keep recieving errors when we try and use the lsqcurvefit function to estimate heat transfer coefficent and thermal conductivity. T is tempature and xt is Time and location. h and k are inital guesses. First function works fine but having errors with second function. Any help would be greatly apreciated.

clear all

close all

clc

%calling data from txt file

tab = importdata('data4.txt');

Time0 = tab (:,1); %time

Time1 = [Time0 Time0 Time0 Time0 Time0 Time0];

Time = Time1(:);

TCB = tab(:,2); %Thermo Base

TC1 = tab(:,3); %Thermo 1

TC2 = tab(:,4); %Thermo 2

TC3 = tab(:,5); %Thermo 3

TC4 = tab(:,6); %Thermo 4

TC5 = tab(:,7); %Thermo 5

t = [TCB TC1 TC2 TC3 TC4 TC5];

T = t(:);

U = tab(:,8); %PID Gain

x0 = tab(:,9); %Distance

x1 = tab(:,10); %Distance

x2 = tab(:,11); %Distance

x3 = tab(:,12); %Distance

x4 = tab(:,13); %Distance

x5 = tab(:,14); %Distance

j = [x0 x1 x2 x3 x4 x5];

X = j(:);

xt = [X,Time];

% Knowns/IGuesses

T_amb = 26; % ambient Temperature in Celcius

T_base = 75; % set temperature of the heating element/base

rho = 7860; % density

d = 0.003175; % diameter

c = 500; % specific heat J/kg*Celcius

s = pi*d; % permimeter in meters

A = pi*d^2/4; % cross sectional area in meters squared

h = 132.918; % heating coefficient Guessed

k = 14; % thermal conductivity Guessed

L = 0.2032; % length of rod being used (to last thermcouple) in meters

alpha_guess = .04;

fun = @(y)((y(1)).*(1-exp(-y(2).*Time0)))-TCB

guess = [T_base,alpha_guess];

options.Algorithm = 'levenberg-marquardt';

y = lsqnonlin(fun, guess, [], [], options)

alpha = y(2);

T0 = y(1); %Tbase - Tamb

syms n

kappa = @(x,xt)x(2)/(rho*c);

v = @(x,xt)(x(1)*s)/(rho*A*c);

Bn = @(x,xt)((2*n-1)*pi*sqrt(kappa(x,xt)))/(2*L);

a = @(x,xt)((4*T0)/((2*n-1)*pi));

b = @(x,xt)(v(x,xt)/(v(x,xt)+(Bn(x,xt)^2)));

c = @(x,xt)(1-exp(-((Bn(x,xt)^2)+v(x,xt))*xt(:,2)));

d = @(x,xt)((v(x,xt)-alpha)/(v(x,xt)-alpha+(Bn(x,xt)^2)));

e = @(x,xt)(exp(-alpha*xt(:,2))-exp(-((Bn(x,xt)^2)+v(x,xt))*xt(:,2)));

f = @(x,xt)(sin((Bn(x,xt)*xt(:,1))/sqrt(kappa(x,xt))));

gx = @(x,xt)(a(x,xt)*(b(x,xt)*c(x,xt)-d(x,xt)*e(x,xt)).*f(x,xt));

fun1 = @(x,xt)(T0*(1-exp(-alpha*xt(:,2)))-symsum(gx(x,xt)));

guess1 = [h,k];

options.Algorithm = 'levenberg-marquardt';

lsqcurvefit(fun1,guess1,xt,T)

Heat_transfer_coefficient = x(1)

Thermal_conductivity_coefficient = x(2)

Error using sym/symsum (line 81)

Error using maplemex

Error, (in factor) floating point coefficients are incompatible with field extension; use 'real' or 'complex' instead

Error in Frank>@(x,xt)(T0*(1-exp(-alpha*xt(:,2)))-symsum(gx(x,xt)))

Error in lsqcurvefit (line 213)

initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});

Error in Frank (line 70)

lsqcurvefit(fun1,guess1,xt,T)

Caused by:

Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.