Gmx hydorder command output error hi (1.500000) <= lo (1.500000)

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Hello everyone.,
I am using the command gmx hydorder for analyzing tetrahedrality order parameter in my system. However , I am getting the following error :
Command line:
gmx hydorder -f npt.trr -s npt.tpr -n index.ndx -o int1.xpm int2.xpm -b 0 -e 100

Taking z axis as normal to the membrane
Reading file npt.tpr, VERSION 2018.1 (single precision)
Reading file npt.tpr, VERSION 2018.1 (single precision)
Select the group that contains the atoms you want to use for the tetrahedrality order parameter calculation:
Group 0 ( System) has 5613 elements
Group 1 ( Water) has 5472 elements
Group 2 ( SOL) has 5472 elements
Group 3 ( non-Water) has 141 elements
Group 4 ( Other) has 141 elements
Group 5 ( CO2) has 141 elements
Group 6 ( OW) has 1368 elements
Group 7 ( C1) has 47 elements
Select a group: 2
Selected 2: ‘SOL’
trr version: GMX_trn_file (single precision)
Last frame 40 time 40.000

Program: gmx hydorder, version 2018.1
Source file: src/gromacs/fileio/matio.cpp (line 1172)

Fatal error:
hi (1.500000) <= lo (1.500000)

For more information and tips for troubleshooting, please check the GROMACS
website at Common Errors — GROMACS webpage documentation

Can anyone please help how to solve this error ?