Deleting slices in 3D array structure containing cell array fields

I have several 3D structures with the following notation

Array(1:17,1:10,1:50).fields{1,1:10}(2,:)

I need to delete the contents of the followinf slices in all the fields of all the arrays

Array([9 11],[2 5 10],[16 30]).fields

I have tried several codes but I get different errors such as:

Deletion requires an existing variable. 
Expected one output from a curly brace or dot indexing expression, but there were 500 results.
Subscripted assignment dimension mismatch. 

I have tried, compressed code, for loops, eval, alternatives to not use eval but nothing works. Here is my last code:

ite= {'test_targets', 'test_inputs', 'predicted_outputs', 'perf', 'abs_error_angle', 'abs_error_moment', 'RMSE_angle', 'RMSE_moment'};
condition ={'narxwalk','EMG1walk','EMG2walk','EMGwalk','vel1walk','vel2walk','vel3walk','inputswalk','anglewalk', 'momentwalk', 'outputswalk', 'narxup', 'EMG1up', ...
    'EMG2up','EMGup','vel1up','vel2up','vel3up','inputsup','angleup','momentup','outputsup','narxdown','EMG1down','EMG2down','EMGdown','vel1down','vel2down', ...
    'vel3down','inputsdown','angledown','momentdown','outputsdown','velwalk','EMGoutwalk','veloutwalk','velup','EMGoutup','veloutup','veldown','EMGoutdown', 'veloutdown'};

for i = 1:length(ite)
    for pi = [9 11]
        for sw = [2 5 10]
            for hL = [16 30]
                for K = 1 : length(condition)
                    if isempty(eval([ite{i},'(',num2str(pi),',',num2str(sw),',',num2str(hL),').',condition{K}]))
                        continue
                    else
                        eval([ite{i},'(',num2str(pi),',',num2str(sw),',',num2str(hL),').',condition{K}])=[];
                    end
                end
            end
        end
    end
end

But I get

Deletion requires an existing variable. 

But I know the variable exists because if I check

eval([ite{i},'(',num2str(pi),',',num2str(sw),',',num2str(hL),').',condition{K}])

it does show the contents of the structure.

I don't know that I am missing.

Thank you.