Singularity in Pulay matrix - what does this error means ?


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Gets Around
Hi,

I'm trying to perform a DFT calculation but it is not converging. Can you please tell me what is wrong here.
The code I'm using is:
title 'energy'
start dimer
geometry units angstrom
  #symmetry c1
  N -8.062 1.363 3.105;H -8.891 1.584 3.159;N -13.919 2.967 8.462;C -13.035 3.498 9.280
end
basis "ao basis"
  * library 6-311+g*
   bqN library N 6-311+g*
  bqH library H 6-311+g*
  bqO library O 6-311+g*
  bqC library C 6-311+g*
end
dft  
  odft 
  xc m06-2x
  direct
  grid fine
  mult 2
  #convergence energy 1e-8
  iterations 10000
end
bsse
  mon first 1 2 
  mon second 3 4
  mult 2
end
task dft energy


After 5000 steps it keep saying "Singularity in Pulay matrix. Error and Fock matrices removed." during the convergence. But never finishes successfully.
   convergence    iter        energy       DeltaE   RMS-Dens  Diis-err    time
 ---------------- ----- ----------------- --------- --------- ---------  ------
 d= 0,ls=0.0          1               NaN       NaN  5.34D-02               0.6
                                                     4.11D-02
 d= 0,ls=0.0          2    -46.6163595845       NaN  7.44D-02               0.8
                                                     5.83D-02
 d= 0,ls=0.0,diis     3-788843.7114149755 -7.89D+05  2.17D+00  2.58D+15     1.1
                                                     9.09D-02  1.41D+01
  Singularity in Pulay matrix. Error and Fock matrices removed. 
 d= 0,ls=0.5,diis     4    -79.3380516151  7.89D+05  2.17D+00  4.16D+00     1.4
                                                     1.16D-01  7.04D+00
  Singularity in Pulay matrix. Error and Fock matrices removed. 
 d= 0,ls=0.5,diis     5******************  1.57D+07  1.20D-01  2.09D+01     1.6
                                                     1.09D+00  1.41D+17
  Singularity in Pulay matrix. Error and Fock matrices removed. 
 d= 0,ls=0.5,diis     6   -110.4162220371 -1.57D+07  1.25D-01  1.01D+01     1.9
                                                     1.10D+00  5.31D+00
 d= 0,ls=0.5,diis     7   3668.9152020524  3.78D+03  5.89D-04  2.56D+06     2.1


Little bit suggestions on the issue would be highly appreciated.
thanks.