[gmx-users] grompp error

[Q. Y. HUAN]

 Dear all.
I wanted to run grompp in order to perform Em, but it showed me this fatal errer::



Back Off! I just backed up mdout.mdp to ./#mdout.mdp.1#
checking input for internal consistency...
calling /usr/bin/cpp...
processing topology...
Generated 332520 of the 332520 non-bonded parameter combinations
Generating 1-4 interactions: fudge = 0.5
Generated 332520 of the 332520 1-4 parameter combinations
Cleaning up temporary file grompptz9Dth

-------------------------------------------------------
Program grompp_d, VERSION 3.3.3
Source code file: toputil.c, line: 61

Fatal error:
Atomtype 'CH3' not found!
-------------------------------------------------------

what is the error and where the source code file located?

thanks


QIU YI HUAN
A beginner of Gromacs user.