You are using a very old GROMACS version. We always suggest to use the newest version. As versions 2019 and 2020 do not support user tables, this is version 2018. In that version you should be able to change the buffer for the energy group table input by replacing the macro STRLEN by a sufficiently large number (of characters) in egptable[STRLEN] on line 88 in the file src/gromacs/gmxpreprocess/readir.cpp