Insufficiently constrained model problem

[Vicarq]

Hello.
Solving a model y get that error in the last moment, no more errors, no warnings, and I don't know how to fix it.
The model is a little building only made whit SHELL63 elements.
Please help and thanks.
*** ERROR *** CP = 67.096 TIME= 23:46:56
A small negative equation solver pivot term has been encountered at the
UX degree of freedom of node 16076. Check for an insufficiently
constrained model.
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S O L U T I O N O P T I O N S

PROBLEM DIMENSIONALITY. . . . . . . . . . . . .3-D
DEGREES OF FREEDOM. . . . . . UX UY UZ ROTX ROTY ROTZ
ANALYSIS TYPE . . . . . . . . . . . . . . . . .STATIC (STEADY-STATE)
GLOBALLY ASSEMBLED MATRIX . . . . . . . . . . .SYMMETRIC

L O A D S T E P O P T I O N S

LOAD STEP NUMBER. . . . . . . . . . . . . . . . 1
TIME AT END OF THE LOAD STEP. . . . . . . . . . 1.0000
NUMBER OF SUBSTEPS. . . . . . . . . . . . . . . 1
STEP CHANGE BOUNDARY CONDITIONS . . . . . . . . NO
INERTIA LOADS X Y Z
ACEL . . . . . . . . . . . . 0.0000 9.8000 0.0000
PRINT OUTPUT CONTROLS . . . . . . . . . . . . .NO PRINTOUT
DATABASE OUTPUT CONTROLS. . . . . . . . . . . .ALL DATA WRITTEN
FOR THE LAST SUBSTE