Whant's wrong is my erc20 token deploy in solidity remix ide - solidity

Question

Here is my ERC20 implementation code. When I deploy to Ropsten testing network, I can't add token to my metamask by demonstrating token symbol automatically. I still can't send it to the other account in MEW wallet by error message. All of the function in contract follow the erc20 interface.
contract TWTD {
mapping (address => uint256) public ownerTobalance;
mapping (address => mapping (address => uint256)) public allowance;
event Approval(address indexed owner, address indexed spender, uint256 value);
event Transfer(address indexed from, address indexed to, uint256 value);
string TokenName;
string Symbol;
uint8 decimals = 18;
uint256 totalsupply;
using SafeMath for uint256;
function TWTD(string _name, string _symbol, uint256 _initialsupply) public {
ownerTobalance[msg.sender] = _initialsupply;
totalsupply = _initialsupply;
TokenName = _name;
Symbol = _symbol;
}
function totalSupply() public view returns (uint256){
return totalsupply;
}
function balanceOf(address who) public view returns (uint256) {
return ownerTobalance[who];
}
function _transfer(address from, address to, uint256 value) internal {
require ( to != 0x0);
require (ownerTobalance[from] >= value);
uint256 Balance = ownerTobalance[from] + ownerTobalance[to];
ownerTobalance[from].sub(value);
ownerTobalance[to].add(value);
assert(ownerTobalance[from] + ownerTobalance[to] == Balance);
emit Transfer(from,to,value);
}
function transfer(address to, uint256 value) public returns (bool) {
_transfer(msg.sender,to,value);
return true;
}
function transferFrom(address from, address to, uint256 value) public returns (bool) {
require (allowance[from][msg.sender] >= value);
allowance[from][msg.sender].sub(value);
_transfer(from,to,value);
return true;
}
function approve(address spender, uint256 value) public returns (bool) {
require(value > 0);
allowance[msg.sender][spender] = value;
emit Approval(msg.sender,spender,value);
return true;
}
function allowance(address owner, address spender)
public view returns (uint256) {
return allowance[owner][spender];
}
}