Please help for exp rate error

Hello.

My friends can't receive exp from mobs correctly.
This error occurred for ONLY my friends. Then, I have no exp problems.

For example, I receive 798440EXP and 72240JP with Stamina Saver and Growth Potion in Lost Mines.
(Stamina Saver+199610EXP + 18060JP)
(Growth Potion+399220EXP + 36120JP)

But my friends get only 119028EXP and 72240JP with Stamina Saver and Growth Potion in Lost Mines.
(Stamina Saver+29757EXP + 18060JP)
(Growth Potion+59514EXP + 36120JP)

Receiving JP seems to work fine.

NOTE: I and my friends are same lv 40.
Why this error occurred?

This is my setting in the gameserver.opt.

Code:

S app.name:Game Server
S auth.server_idx:1
S auth.server_name:game001
S db.game.ip:127.0.0.1
S db.c._password:
S db.c.account:sa
S db.c.name:Arcadia
S db.c.server:127.0.0.1
S db.user._password:
S db.user.account:sa
S db.user.name:Telecaster
S db.user.server:127.0.0.1
S game.cash_item_dropable:1
S game.iocp.active:1
S game.console.port:4502
S game.server_screenshot_url:
S game.guild_icon_base_url:
S blank.io.port:4502
S log.disable:1
S log.working:0
S io.port:4514
S io.ip_address:127.0.0.1
S io.upload.ip:127.0.0.1
S io.upload.port:4616
S memory.player_heap_size:760
N game.item_hold_time:18000
N game.logout_timer:0
N game.skip_loading_attribute:1
T set_user_limit:1000
T game.use_login_logout_debug:0
T game.mem_usage_info_save_interval:0
T game.cash_usable_server:1
T game.no_collision_check:1
T game.no_skill_cooltime:0
T game.disable_huntaholic:0
T game.PKServer:0
T game.use_auto_jail:0
T game.use_auto_trap:0
T game.disable_dungeon_raid_siege:0
T game.limit_dungeon_enterable_level:0
T game.max_storage_item_count:1000
T game.max_level:170
S game.exp_rate:50
S game.item_drop_rate:5
S game.gold_drop_rate:5
S game.chaos_drop_rate:5

Command set game.exp_rate 50 also doesn't work for only my friends.
And why S game.gold_drop_rate: doesn't work??????

Please someone give me any ideas:(