I'm assuming you're running GunGame5.0, which requires a plugin for respawning to be specified by the
gg_respawn_cmd configurable option in your
../cfg/gungame5/gg_en_config.cfg.
I
HIGHLY recommend that you simply install GunGame5.1 instead though. In GunGame5.1, the required Source Python Extensions plugin handles respawning.
GunGame5.1 Installation Instructions