Problem with Model between Ansys 11 and 15 (APDL)

[maha.moddather.hassan]

Hi,
I have the following simple model determining the plate buckling load. It has been running without a problem in ANSYS apdl 11; however, when using Ansys 15, a message showing that the model is not constrained appears. The model is constrained only in the Z direction and the first buckling mode is neglected. Is there a reason for this?
/FILNAM, MODEL1
/TITLE, C, SOLID PLATE
WPSTYLE,,,,,,,,0
/PREP7
!PARAMETERS
!UNITS , N, MM
T=10 !THICKNESS OF PLATE
W=1000 !WIDTH OF PLATE
D=1000 !DEPTH OF PLATE
OPH= 300 !DIAMETER OF OPENING
OPX= 400 !DISTANCE OF IN X TILL CENTER OF OPENING
OPY= 500 !DISTANCE OF IN Y TILL CENTER OF OPENING
!ELEMENT TYPE
ET,1,SHELL63
!REAL CONSTANT
R,1,T, , , , , ,
!MATERIAL PROPERTIES
! STEEL MATERIAL
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,EX,1,,210000
MPDATA,PRXY,1,,0.3
!GEOMETRY
RECTNG,0,W,0,D,
CYL4,OPX,OPY,OPH/2
ASBA,1,2
!MESHING
LSEL,S,LINE,,2
LSEL,A,LINE,,4
LESIZE,ALL, , ,32, , , , ,1
LSEL,S,LINE,,1
LSEL,A,LINE,,3
LESIZE,ALL, , ,32, , , , ,1
LSEL,S,LINE,,5,8,1
LESIZE,ALL, , ,16, , , , ,1
MSHAPE,0,2D
MSHKEY,2
AMESH,ALL
FINISH
/SOL
! DEFINING DEGREES OF FREEDOM
LSEL,S,LINE,,1,4,1
DL,ALL,1,UZ,0

! DEFINING PRESSURE ON LINES
LSEL,S,LINE,,2
LSEL,A,LINE,,4
SFL,ALL,PRES,1,

ALLSEL,ALL
! SOLUTION CONTROL: FIRST ANALYSIS STAGE
ANTYPE,0
PSTRES,1
/STATUS,SOLU
SOLVE
FINISH
/SOLUTION
ANTYPE,1
BUCOPT,SUBSP,2,0,0 !NUMBER OF CONSIDERED MODES = 2
SUBOPT,0,0,0,0,0,ALL
MXPAND,2,0,0,1,0.001, !NUMBER OF CONSIDERED MODES = 2
/STATUS,SOLU
SOLVE
FINISH

Thanks a lot for your help.
Regards,
Maha Hassan
CUFE