guess you didn't read the error message ?
try removing weapon_ before and just have hegrenade like:
Code:
// This file is where you will list all weapons
// that will be used for the warmup system.
// This file is parsed every map change.
// Weapons should be listed in the following format:
// hegrenade
// glock
// etc
hegrenade
I have weapon_hegrenade in mine but I am using a very old version so I guess they have changed