Warning: Unable to find explicit solution.

I already posted this question, but i got the infromation, that i forget to include relevant information. This function worked until now. I had to change some input parameters and now i get this error: Warning:

Unable to find explicit solution. For options, see help.

In solve (line 317)

In Estimate_p (line 11)

In A_bekannt_agentization_v4_limitedMemory (line 371)

Unable to perform assignment because the left and right sides have a different number of elements.

Error in A_bekannt_agentization_v4_limitedMemory (line 371)

x(3)=Estimate_p(x);

I don't know exactly when this error is happening, because there are 700 *20 times, that this function get's called.

function estimate_p = Estimate_p(x)
syms a;
syms p;
estimate_p=double(solve(subs(diff(DA(a,x(7),x(9)),a),a,x(2))-subs(diff(UAS(x(1),a,p,x(4),x(6),x(10)),a),a,x(2)),p));
clear a;
clear p;
end

function uas = UAS( fl,a,p,productivity,aara,umw )
%aara is not 0. so everytime it's the elses case.
if (aara==0)
    uas=S(fl,a,productivity,p,umw);
else
    uas=(1 - exp(1)^(-aara*S(fl,a,productivity,p,umw)) ) / aara;
end

function da = DA( a, disa, eqeffort )
da=((a*eqeffort)^disa)*0.5;
end

%x(1)=fl
%x(2)=a
%x(3)=p
%x(4)=productivity
%x(5)=para
%x(6)=aara
%x(7)=disa
%x(8)=resutil
%x(9)=eqeffort
%x(10)=umw
fl=0; %constant
productivity=50; %constant
araP=0; %constant
araA=0.5; %constant
disA=2; %constant
resutil=0;%constant
eqeffort=0.01;%constant
umw=0 %at the beginning