求助！静力仿真提示错误there is at least 1 small equation solver....

我在做一个静力分析，模型是上面一个膜，下面一个梯形体，梯形体式建八个关键点然后生成面再生成体，用扫掠法划分了网格（不知道为什么，不能自由划分，纳闷）,对上面的薄膜四个侧边进行约束，在薄膜的上表面施加pressure。计算时候提示错误：there is at least 1 small equation solver pivot term(e.g., at the UZ degree of freedom of node 5885), please check for an insufficiently constrained model. 我的约束就是膜的四个侧边啊，为什么总出错。求助！
附程序：
/PREP7
ET,1,SOLID95 !The Element Type
MP, EX, 1, 1.7E11 !弹性模量
MP, PRXY, 1, 0.3 !泊松比
MP, DENS, 1, 2.33E3 !密度
K,1,-68e-6,183e-6,0,
K,2,6.8e-005,0.000183,0,
K,3,-6.8e-005,-0.000183,0,
K,4,6.8e-005,-0.000183,0,
K,5,-125e-6,240e-6,80e-6,
K,6,0.000125,0.00024,8e-005,
K,7,-0.000125,-0.00024,8e-005,
K,8,0.000125,-0.00024,8e-005,
FLST,2,3,3
FITEM,2,5
FITEM,2,1
FITEM,2,3
A,P51X
FLST,2,3,3
FITEM,2,5
FITEM,2,7
FITEM,2,3
A,P51X
FLST,2,3,3
FITEM,2,5
FITEM,2,1
FITEM,2,2
A,P51X
FLST,2,3,3
FITEM,2,5
FITEM,2,2
FITEM,2,6
A,P51X
FLST,2,3,3
FITEM,2,2
FITEM,2,4
FITEM,2,8
A,P51X
FLST,2,3,3
FITEM,2,2
FITEM,2,6
FITEM,2,8
A,P51X
FLST,2,3,3
FITEM,2,3
FITEM,2,4
FITEM,2,7
A,P51X
FLST,2,3,3
FITEM,2,7
FITEM,2,4
FITEM,2,8
A,P51X
FLST,2,3,3
FITEM,2,5
FITEM,2,7
FITEM,2,8
A,P51X
FLST,2,3,3
FITEM,2,6
FITEM,2,5
FITEM,2,8
A,P51X
FLST,2,3,3
FITEM,2,4
FITEM,2,2
FITEM,2,3
A,P51X
FLST,2,3,3
FITEM,2,1
FITEM,2,2
FITEM,2,3
A,P51X
FLST,2,12,5,ORDE,2
FITEM,2,1
FITEM,2,-12
VA,P51X
FLST,2,2,5,ORDE,2
FITEM,2,9
FITEM,2,-10
AADD,P51X
FLST,2,2,5,ORDE,2
FITEM,2,11
FITEM,2,-12
AADD,P51X
FLST,2,2,5,ORDE,2
FITEM,2,5
FITEM,2,-6
AADD,P51X
FLST,2,2,5,ORDE,2
FITEM,2,1
FITEM,2,-2
AADD,P51X
FLST,2,2,5,ORDE,2
FITEM,2,7
FITEM,2,-8
AADD,P51X
FLST,2,2,5,ORDE,2
FITEM,2,3
FITEM,2,-4
AADD,P51X
BLOCK,-400e-6,400e-6,-400e-6,400e-6,80e-6,110e-6,
FLST,2,2,6,ORDE,2
FITEM,2,1
FITEM,2,-2
VGLUE,P51X
FLST,2,2,5,ORDE,2
FITEM,2,12
FITEM,2,-13
AADD,P51X
EXTOPT,VSWE,AUTO,0
EXTOPT,ESIZE,4,0
FLST,5,2,4,ORDE,2
FITEM,5,4
FITEM,5,13
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1,20e-6, ,24, , , , ,0
!*
FLST,5,2,4,ORDE,2
FITEM,5,9
FITEM,5,16
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1,25e-6, ,10, , , , ,0
VSWEEP,1,13,9
EXTOPT,ESIZE,3,0
FLST,5,2,4,ORDE,2
FITEM,5,7
FITEM,5,15
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1,25e-006, ,32, , , , ,0
!*
FLST,5,2,4,ORDE,2
FITEM,5,3
FITEM,5,18
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1,20e-006, ,40, , , , ,0
VSWEEP,3,3,4
/SOL
ANTYPE,0
FLST,2,4,5,ORDE,3
FITEM,2,6
FITEM,2,-8
FITEM,2,11
/GO
DA,P51X,ALL,0
FLST,2,1,5,ORDE,1
FITEM,2,4
/GO
SFA,P51X,1,PRES,1.5E6
SOLVE