Problems with fitting

I am trying to perform a fitting and I am obtaining the following results

parTLi1 = [tmaxi,imaxi,eacti1];

F1=@(temp,parTLi1)(…);

wt_tl=ones(size(temp));
iter_tl=800;
tol_tl=0.1;
dFdp_tl=“dfdp”;
dp_tl=0.0001*ones(size(parTLi1));

f2=0;

[f2, pfit1, kvg, iter, corp1, covp1, covr1] = leasqr (temp, intensity, parTLi1, F1,tol_tl, iter_tl,wt_tl, dp_tl, dFdp_tl);

kvg = 1
iter = 3
corp1 =

NA    NA    NA
NA    NA    NA
NA    NA    NA

covp1 =

NA    NA    NA
NA    NA    NA
NA    NA    NA

¿could you help me?

Was it possible to send a more complete runnable example with input data?