when your character are muted, it cant use command or chat.
try replace the atcommand with these
sc_start SC_MUTE, 10800000, 0;
sc_end SC_MUTE;
if you want a better approach, then use the setpcblock instead.
*setpcblock <type>,<state>{,<account ID>};
*getpcblock {<account ID>};
'setpcblock' command prevents/allows the player from doing the given <type> of action according
to the <state> during the player session (note: @reloadscript removes all <type> except PCBLOCK_IMMUNE).
The <type> values are bit-masks, multiples of <type> can be added to change the player action.
The action is blocked when the <state> is true, while false allows the action again.
'getpcblock' command return the bit-mask value of the currently
enabled block flags.
Available <type>:
PCBLOCK_MOVE Prevent the player from moving.
PCBLOCK_ATTACK Prevent the player from attacking.
PCBLOCK_SKILL Prevent the player from using skills/itemskills.
PCBLOCK_USEITEM Prevent the player from using usable items.
PCBLOCK_CHAT Prevent the player from sending global/guild/party/whisper messages.
PCBLOCK_IMMUNE Prevent the player from being hit by monsters.
PCBLOCK_SITSTAND Prevent the player from sitting/standing.
PCBLOCK_COMMANDS Prevent the player from using atcommands/charcommands.
PCBLOCK_NPCCLICK Prevent the player from clicking/touching any NPC/shop/warp.
PCBLOCK_EMOTION Prevent the player from using emotions.
PCBLOCK_NPC Simulate NPC interaction. Useful for NPC with no mes window. Sum of PCBLOCK_MOVE|PCBLOCK_SKILL|PCBLOCK_USEITEM|PCBLOCK_COMMANDS|PCBLOCK_NPCCLICK.
PCBLOCK_ALL Sum of all the flags.
Examples:
// Make the attached player invulnerable to monster (same as @monsterignore)
setpcblock PCBLOCK_IMMUNE, true;
// Prevents the attached player from attacking and using skills
setpcblock PCBLOCK_ATTACK|PCBLOCK_SKILL, true;
// Re-enables attack, skills and item use
setpcblock PCBLOCK_ATTACK|PCBLOCK_SKILL|PCBLOCK_USEITEM, false;
// getpcblock related checks
if (getpcblock() & PCBLOCK_IMMUNE)
mes "You are invulnerable!";
if (getpcblock() & (PCBLOCK_MOVE|PCBLOCK_SITSTAND))
mes "You can't walk or sit.";
if ((getpcblock() & (PCBLOCK_ATTACK|PCBLOCK_SKILL)) == 0)
mes "You can attack and use skills.";
if (getpcblock() & PCBLOCK_CHAT)
mes "You can't chat.";