Illegal operation: - {log-concave}

the goal function is minimize( sum(1-exp(-(x(1:N+1)).^2/delta^2) ) ),
then cvx appear Disciplined convex programming error:
Illegal operation: - {log-concave}
please tell me what is meaning of the above error

FAQ: Why doesn’t CVX accept my problem? [READ THIS FIRST]

hello , Sorry but how can we overcome such an errors like this ?

Error using cvx/power (line 115)
Disciplined convex programming error:
Cannot perform the operation {positive constant}.^{concave}

Error in cvx/mpower (line 9)
z = power( x, y );

Error in Algorithm (line 32)
YoA >= 2^(2a1U)-1;

or errors that occurs when we are using log functions ?

Read the FAQ, please.