Registration Problem

<?php
	if(isloggedin($_POST['username']))
	{
		echo "<div class='alert alert-error'>You are already logged in!</div>";
	}
	else
	{
	if(isset($_POST['username']) && isset($_POST['password']) && isset($_POST['passwordagain']) && isset($_POST['email']))
	{
		if(!empty($_POST['username']) && !empty($_POST['password']) && !empty($_POST['passwordagain']) && !empty($_POST['email']))
		{
			//defineing variables
			$username = $_POST['username'];
			$password = $_POST['password'];
			$passwordagain = $_POST['passwordagain'];
			$email = $_POST['email'];
			if(ctype_alnum($username) && ctype_alnum($password) && ctype_alnum($passwordagain) && filter_var($email, FILTER_VALIDATE_EMAIL))
			{
				if(strlen($username)>=6 && strlen($password)>=6 && strlen($passwordagain)>=6 && strlen($email)>=6)
				{
					//passwords match
					if($password == $passwordagain)
					{
						$emailexistcommand = "SELECT * FROM TACCOUNT WHERE szMail = '$email'";
						$emailexistquery = odbc_exec($TGLOBALdatabase, $emailexistcommand);
						if(!odbc_num_rows($emailexistquery))
						{
							$userexistcommand = "SELECT * FROM TACCOUNT WHERE szUserID = '$username'";
							$userexistquery = odbc_exec($TGLOBALdatabase, $userexistcommand);
							if(!odbc_num_rows($userexistquery))
							{
								$salt = generateSalt();
								$userregistercommand = "INSERT INTO TACCOUNT (szUserID, szPasswd, bCheck, szSalt, szMail, dwActive, dwAdmin) VALUES (?, ?, ?, ?, ?, ?, ?)";
								$userregisterprepare = odbc_prepare($TGLOBALdatabase, $userregistercommand);
								$userregisterquery = odbc_execute($userregisterprepare, array($username,$password,0,$salt,$email, 0, 0));
								$userquerycommand = "SELECT * FROM TACCOUNT WHERE szUserID = '$username'";
								$userquery = odbc_exec($TGLOBALdatabase, $userquerycommand);
								$userinfo = odbc_fetch_array($userquery);
								$userid = $userinfo['dwUserID'];
								$usercashcommand = "INSERT INTO TCASHTESTTABLE (dwUserID, dwCash, dwBonus) VALUES (?, ?, ?)";
								$usercashprepare = odbc_prepare($TGLOBALdatabase, $usercashcommand);
								$usercashquery = odbc_execute($usercashprepare, array($userid, 0, 0));
								addItem($userid,9,10);
								addItem($userid,66,5);
								addItem($userid,100,3);
								addItem($userid,96,2);
								addItem($userid,330,3);
								mail($email, '4Story - Register - NoReply', 'You have succesfully registred an account!To activate your account please visit:http://localhost/account/validate.php?id=' . $userinfo['dwUserID'] . '&code=' . $salt);
								echo "<div class='alert alert-success'>You succesfully registred!We sent the activation email to your emailTo activate your account please visit: <a href='http://localhost/account/validate.php?id=" . $userinfo['dwUserID'] . "&code=" . $salt . "'>this</a></div>";
							}
							else
							{
								echo "<div class='alert alert-error'>This username is already taken!</div>";
							}
						}
						else
						{
							echo "<div class='alert alert-error'>This email is already taken!</div>";
						}
					}
					else
					{
						echo "<div class='alert alert-error'>Passwords must match!</div>";
					}
				}
				else
				{
					echo "<div class='alert alert-error'>Username and password must be more than 6 characters!</div>";
				}
			}
			else
			{
				echo "<div class='alert alert-error'>You can use only alphanumerical characters!</div>";
			}
		}
		else
		{
			echo "<div class='alert alert-error'>You must fill in everything!</div>";
		}
	}
	echo '<form id="login" action="/account/register.php" method="POST">
	<input name="username" type="text" placeholder="Username" class="account"></input><small>*Must be at least 6 characters long and alphanumeric</small><br \>
	<input name="password" type="password" placeholder="Password" class="account"></input><small>*Must be at least 6 characters long and alphanumeric</small><br \>
	<input name="passwordagain" type="password" placeholder="Password again" class="account"></input><small>*Must match with first password</small><br \>
	<input name="email" type="text" placeholder="E-mail" class="account"></input><small>*Must be a valid email address</small><br \>
	<input type="submit" class="registerbtn" style="float:left;margin-left:20px;" value="submit" class="submit" /><br \>
	</form>';
	}
?>