# Syntax error - File forcefield.itp, line 18

**URL:** <https://gromacs.bioexcel.eu/t/syntax-error-file-forcefield-itp-line-18/8670>\
**Category:** User discussions\
**Tags:** grompp\
**Created:** [March 21, 2024, 8:13pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-file-forcefield-itp-line-18/8670 "2024-03-21T20:13:17Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![saikat0003](https://avatars.discourse-cdn.com/v4/letter/s/a4c791/32.png) [@saikat0003](https://gromacs.bioexcel.eu/u/saikat0003)\
**Post date:** [March 21, 2024, 8:13pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-file-forcefield-itp-line-18/8670/1 "2024-03-21T20:13:17Z")

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GROMACS version:2021.4  
GROMACS modification: No  
I’m attempting to run a protein-ligand complex following a tutorial I found at [[Protein-Ligand Complex](http://www.mdtutorials.com/gmx/complex/index.html)]. The only alteration I made was using ligpargen [[https://traken.chem.yale.edu/ligpargen/](https://traken.chem.yale.edu/ligpargen/)] instead. Despite reading through many discussions on the GROMACS forum, I’m still encountering the same issue.

**Fatal error:**  
**Syntax error - File forcefield.itp, line 18**  
**Last line read:**  
**‘[defaults]’**  
**Invalid order for directive defaults**

**For more information and tips for troubleshooting, please check the GROMACS**  
**website at [Common Errors — GROMACS webpage https://www.gromacs.org documentation](http://www.gromacs.org/Documentation/Errors)**

[jz4.top](https://gromacs.bioexcel.eu/uploads/short-url/qM1Gac5AG219cDiztRoXH8azEVh.top) (2.3 KB)  
[topol.top](https://gromacs.bioexcel.eu/uploads/short-url/sjjVAJwZykZ05GJWoiyxEKFYkRT.top) (598 Bytes)  
[jz4.dat](https://gromacs.bioexcel.eu/uploads/short-url/2XOMXgV7Knq01zLQurDn4oViVSd.dat) (11.4 KB)

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<div class="post-metadata">

**Author:** ![scinikhil](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/scinikhil/32/3483_2.png) [@scinikhil](https://gromacs.bioexcel.eu/u/scinikhil)\
**Post date:** [March 21, 2024, 9:02pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-file-forcefield-itp-line-18/8670/2 "2024-03-21T21:02:14Z")

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[https://manual.gromacs.org/2020.2/user-guide/run-time-errors.html#invalid-order-for-directive-xxx](https://manual.gromacs.org/2020.2/user-guide/run-time-errors.html#invalid-order-for-directive-xxx)