Ansys Error what's going on ???

Dear All,

I have much problem when modelling my project with ANSYS, one of problem that I met always like this 

 *** ERROR ***                           CP =     296.828   TIME= 14:56:15
 A small negative equation solver pivot term has been encountered at the
 ROTZ degree of freedom of node 11758.  Check for an insufficiently     
 constrained model.

purpose of my project is to analysis stress distribution in welded tubular joint with MPC (combine between solid element "weld" and shell element "chord & brace")....

 Help me please ...... Really I need help

this is command that I put in ANSYS

/prep7
/units,si
----------    !weld
et,1,186
et,2,181
keyopt,2,3,2
et,3,170
keyopt,3,5,4
et,4,174
keyopt,4,4,2
keyopt,4,5,3
mp,ex,1,2.5E8
mp,prxy,1,.3
mp,dens,1,7850
r,1,0.01128
cylind,0.19172,0.203,-2.065,2.065,0,90
wprota,,-45
cylind,0.07556,0.07,0,2.2402,-90,90
csys,4
agen,2,3,,,,,0.015
vsba,2,13
vdele,4,,,1
vsba,1,15
vdele,2,,,1
vsba,3,20
vdele,1,,,1
cylind,0.0872,0.091,0,1,-90,90
vsba,4,7
vdele,5,,,1
vdele,1,,,1
vglue,2,3
l,24,27
l,21,28
al,2,3,41
al,1,4,39
al,4,36,44,3
va,4,7,8,9,23
vglue,1,2,4
----------    !brace
cylind,0.07,0.07278,0,2.2482,-90,90
vsba,1,18
vdele,2,,,1
vdele,4
adele,28,30,,1
adele,2,26,26-2,1
----------    !chord
wprota,,45
cylind,0.19172,0.19736,-2.065,2.065,-90,90
vsba,1,17
vsba,2,15
vdele,4
vdele,7,,,1
vdele,1
adele,3,31,31-3,1
adele,19,,,1
adele,24,28,2,1
adele,1,2,,1
adele,9,29,29-9,1
----------    !meshing setting
smrtsize,1
vsel,s,,,5,6
vatt,1,,1
vsweep,5
vsweep,6
vsel,s,,,3
vatt,1,,1
extopt,aclear,0
vsweep,3

aatt,1,1,2
mshkey,2
mshape,0,2d
lesize,30,,,20
lesize,8,,,20
lesize,15,,,40
amesh,27,30,3
amesh,4
----------    !MPC setting
type,3
real,2
asel,s,,,17,18
asel,a,,,15
nsla,s,1
esurf
type,4
real,2
lsel,s,,,25,29,4
lsel,a,,,51
nsll,s,1
esurf
----------    !load and pedestal setting
/solu
local,11,0,0,0,0,0,-45
f,4114,fz,2.5E+6
csys
lsel,s,,,8,10,2
dl,all,,ux
dl,all,,uy
dl,all,,uz
dl,all,,rotx
dl,all,,roty
dl,all,,rotz
alls
solve