I'm trying to calculate the zero of a function, and keep getting "Function 'subsindex' not defined for values of class 'struct'" error?

I'm trying to calculate the zero of the function F_net and assign it to the variable omega_zero(ii) in the following program:

slope_list_deg=linspace(-10,35,25);
rover=struct('wheelm',1,'motorm',5,'sciencepayloadm',75,'rtgm',90,'chassism',659,'speedreducerm',1.5,'wheel_radius',.3);
planet=struct('acceleration_grav',3.72);

for ii = 1:length(slope_list_deg)

     omega_zero(ii) = fzero(@(omega_z) F_net(omega_z,slope_list_deg(ii),rover,planet,Crr),1);

end

However, I keep getting the following error:

Error using fzero (line 289)
FZERO cannot continue because user supplied function_handle ==> @(omega_z)F_net(omega_z,slope_list_deg(ii),rover,planet,Crr) failed with the error
below.

   Function 'subsindex' is not defined for values of class 'struct'.

Error in analysis_terrain_slope (line 7)
   omega_zero(ii) = fzero(@(omega_z) F_net(omega_z,slope_list_deg(ii),rover,planet,Crr),1);

I can't figure out where the problem is can anyone help?

[Star Strider]

It would help to know what ‘F_net’ is and what it does. (If it’s a huge function file, attach it using the ‘paperclip’ or ‘staple’ icon instead of posting it in a Comment.)

Is there any particular reason you’re using structures ( e.g. instead of cells )?