Some error when I try to solve a matricial system

[Isabel Gil]

Hello PETSc's users,

I have just started to use PETSc and when I try to solve the matricial 
system I obtain the following error sentences:

[0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 538 in 
src/mat/impls/aij/seq/aijfact.c
[0]PETSC ERROR: Detected zero pivot in LU factorization
see 
http://www.mcs.anl.gov/petsc/petsc-2/documentation/troubleshooting.html#ZeroPivot!
[0]PETSC ERROR: Zero pivot row 277017 value 2.16144e-10 tolerance 1e-12 
* rs 526.244!
[0]PETSC ERROR: MatLUFactorNumeric() line 1843 in src/mat/interface/matrix.c
[0]PETSC ERROR: PCSetUp_ILU() line 854 in src/ksp/pc/impls/ilu/ilu.c
[0]PETSC ERROR: PCSetUp() line 797 in src/ksp/pc/interface/precon.c
[0]PETSC ERROR: KSPSetUp() line 232 in src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 747 in 
src/ksp/pc/impls/bjacobi/bjacobi.c
[0]PETSC ERROR: PCSetUpOnBlocks() line 830 in src/ksp/pc/interface/precon.c
[0]PETSC ERROR: KSPSetUpOnBlocks() line 156 in 
src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: KSPSolve() line 344 in src/ksp/ksp/interface/itfunc.c

I would be really grateful if you could say to me where the problem 
could be in order to sort it out.

Thanks in advance and best regards
Isa