Dextran molecule equillibriation error

[Vignesh666d]

I have generated the dextran molecule of 45 monomers. 1) Monomers were not linked continuously to form a single chain I tried giving dens and box both I am getting two parts 2) I tried to energy minimize it and try to run equilibration I am getting this error: Warning: Only triclinic boxes with the first vector parallel to the x-axis and the second vector in the xy-plane are supported.
Box (3x3):
Box[ 0]={ nan, nan, nan}
Box[ 1]={ nan, nan, nan}
Box[ 2]={ nan, nan, nan}
Can not fix pbc.

Warning: Only triclinic boxes with the first vector parallel to the x-axis and the second vector in the xy-plane are supported.
Box (3x3):
Box[ 0]={ nan, nan, nan}
Box[ 1]={ nan, nan, nan}
Box[ 2]={ nan, nan, nan}
Can not fix pbc.

---

Program: gmx mdrun, version 2021.3
Source file: src/gromacs/mdlib/sim_util.cpp (line 526)

Fatal error:
Step 100: The total potential energy is nan, which is not finite. The LJ and
electrostatic contributions to the energy are 0 and 0, respectively. A
non-finite potential energy can be caused by overlapping interactions in
bonded interactions or very large or Nan coordinate values. Usually this is
caused by a badly- or non-equilibrated initial configuration, incorrect
interactions or parameters in the topology. I used the pre-NPT.mdp file.kindly help me.

[fgrunewald]

Did you run the energy minization with flexible bonds?

[Vignesh666d]

No sir, I didn't use it. I tried with it worked fine. Thank you, sir. @fgrunewald