Error, (in DEtools/convertsys) internal error

Digits := 20:
R0 := 1:
r0k := 0.022: r0n := 0.002: 
mu := 0.005*10^(-4): K := 0.0265:
Tn:=12.5*10^(-4):
 
dsys2 := 0.5*mu* ( (y2(r0)/r0)^(-2) - (diff(y2(r0),r0)*cs0(r0)/cos(y1(r0)) )^(-2) ) + K*( B0(r0)*diff(y2(r0),r0)*y2(r0)/cos(y1(r0)) - 1 ) = (0.5*qn*(y2(r0)^2 - (sin(tet1)*R1)^2) + Tn*(sin(tet1)*R1)*sin(tet1))/( y2(r0)*sin(y1(r0)) ),
     0.5*mu* ( (y2(r0)/r0)^(-2) - (diff(y2(r0),r0)*cs0(r0)/cos(y1(r0)))^(-2) ) * ( diff(y1(r0),r0)*cos(y1(r0))/diff(y2(r0),r0) - sin(y1(r0))/y2(r0) ) + K*(B0(r0)*diff(y2(r0),r0)*y2(r0)/cos(y1(r0)) - 1) * (diff(y1(r0),r0)*cos(y1(r0))/diff(y2(r0),r0) + sin(y1(r0))/y2(r0) )  = qn,
       diff(y3(r0),r0)= diff(y2(r0),r0)*tan(y1(r0)): 
 
gtet2 := proc(tet1,z0,qn,R1) 
local init1,dsol1,tetk;  
global fy3,fy4,fy5;                                                                 
description " Calculation end tet";                                                                              
init1 := y1(r0n) = tet1, y2(r0n) = sin(tet1)*R1, y3(r0n) = z0 ;                                   
dsol1 := dsolve({dsys2,init1},{y1(r0),y2(r0),y3(r0)}, numeric, method=lsode[backfull],output=listprocedure);                
fy3:=rhs(dsol1[2]): fy4 := rhs(dsol1[3]): fy5 := rhs(dsol1[4]): tetk := fy3(0.99999)  
end proc:     
 
tet1 := theta0n;
z0 := 0;
qn := A[1,1];
R1 := Rdef[1,1];
                 
gtet2(tet1,z0,qn,R1);