# Getting an 'error' during Ligand topology steps!

**URL:** <https://gromacs.bioexcel.eu/t/getting-an-error-during-ligand-topology-steps/4773>\
**Category:** User discussions\
**Created:** [September 12, 2022, 7:27am UTC](https://gromacs.bioexcel.eu/t/getting-an-error-during-ligand-topology-steps/4773 "2022-09-12T07:27:10Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![M.Rageh](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@M.Rageh](https://gromacs.bioexcel.eu/u/M.Rageh)\
**Post date:** [September 12, 2022, 7:27am UTC](https://gromacs.bioexcel.eu/t/getting-an-error-during-ligand-topology-steps/4773/1 "2022-09-12T07:27:11Z")

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GROMACS version: 2020.1  
GROMACS modification: Yes/No  
Here post your question

 ![image](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/1/146ede1e8bc5d3ac69420b60dbef507948d3de0d.png)

I need some help, were stucked with this command:  
python3 cgenff\_charmm2gmx\_py3\_nx2.py FAD FAD\_fix.mol2 FAD.str charmm36-jul2021.ff

Note: sudo apt openbabel and pip install networkx==2.1 are all previously done!  
The .str file is generated through CGenFF server…

Thank you in advance

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**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\
**Post date:** [September 12, 2022, 11:15am UTC](https://gromacs.bioexcel.eu/t/getting-an-error-during-ligand-topology-steps/4773/2 "2022-09-12T11:15:46Z")

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This is a generic Python error (try Google :)

You need to install Numpy.

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**Author:** ![M.Rageh](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@M.Rageh](https://gromacs.bioexcel.eu/u/M.Rageh)\
**Post date:** [September 12, 2022, 3:04pm UTC](https://gromacs.bioexcel.eu/t/getting-an-error-during-ligand-topology-steps/4773/3 "2022-09-12T15:04:35Z")

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It worked!!! You are really an expert !!! Thaaaaank you…