定义节点出现错误，请教一下，附命令流。

想请教一下各位，我定义i+1号节点为什么会出现如图所示的错误呢？附命令流到出错的那一步！万分感谢。
/prep7
et,1,beam4
et,2,link10
mp,ex,1,3.5e10
mp,prxy,1,0.17
mp,dens,1,2500
mp,ex,2,10e15
mp,prxy,2,0
mp,dens,2,0
mp,ex,3,1.9e10
mp,prxy,3,0.25
mp,dens,3,1200
r,1,16,1.6,25.6,2000,20,21.8
r,2,4.7,3.4,16,39.7,77,7,61.6
r,3,9,6,54,200,450,61.6
r,4,8,5,40,83.3,213.3,333.3
r,5,1,1,1,1/12,1/12,1/3
r,6,,,0.012
*do,i,1,59
x=-174*2+(i-1)*6
y1=-14
y2=14
n,3*(i-1)+1,x
n,3*(i-1)+2,x,y1
n,3*i,x,y2
*enddo
/prep7
type1
real,1
mat,1
*do,i,1,58
j=3*(i-1)+1
e,j,j+3
*enddo
finish
/prep7
type,1
real,5
mat,2
*do,i,1,59
j=3*(i-1)+1
j1=3*(i-1)+2
j2=3*i
e,j,j1
e,j,j2
*enddo
finish
i=59*3
n,i+1,-174,-10,-30