objpcgel.o: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/x86_64-linux-gnu/gap/bin/objpcgel.o - from package: gap-dev

You may install the required package with command apt-get install {package}

Error in other languages:
objpcgel.o: bevel nie gevind nie
objpcgel.o: comandă negăsită
objpcgel.o: comando não encontrado
objpcgel.o: commande introuvable
objpcgel.o: command not found
objpcgel.o: käsku ei ole
objpcgel.o: không tìm thấy lệnh
objpcgel.o: komanda nerasta
objpcgel.o: Kommando nicht gefunden.
objpcgel.o: kommandot finns inte
objpcgel.o: komut yok
objpcgel.o: nie znaleziono polecenia
objpcgel.o: níor aimsíodh an t-ordú
objpcgel.o: no se encontró la orden
objpcgel.o: no s'ha trobat l'ordre
objpcgel.o: opdracht niet gevonden
objpcgel.o: parancs nem található
objpcgel.o: perintah tidak ditemukan
objpcgel.o: príkaz nenájdený
objpcgel.o: příkaz nenalezen
objpcgel.o: команда не найдена
objpcgel.o: командата не е открита
objpcgel.o: 命令找不到
objpcgel.o: コマンドが見つかりません