title: GSM Modem USSD Check Balance Getting CME Error 100
body: <p>I'm trying to check the SIM Card Balance via USSD using Huawei E1550 3G modem</p>
  
  <p>But when i always send </p>
  
  <pre><code>   AT+CUSD=1,"*100#",15
  </code></pre>
  
  <p>I Get </p>
  
  <pre><code>   +CME Error: 100
  </code></pre>
  
  <p>And yes my modem support USSD because i have a dashboard application for the modem and i can check the balance and also recharge the SIM Card.</p>
  
  <p>I'm using GSMComm library in C# i've also tried it in putty termainl but keep getting the same error</p>
  
  <p>I searched for the error 100 and found that it's "Unknown Error" no really helpful :)</p>
  
  <p>I did also tried changing text mode to  pdu mode before sending but nothing changed</p>
  
  <pre><code>   AT+CMGF=0
  </code></pre>
  
  <p>Note:
  I've also tried </p>
  
  <pre><code>  AT+CUSD=1,"*100#"
  </code></pre>
  
  <p>the same error</p>
  
  <p>and the response of </p>
  
  <pre><code>   AT+CUSD=?
  </code></pre>
  
  <p>is </p>
  
  <pre><code>  (0-2)
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I've Converted the request "*100#" to 7bit "2A31303023" like this</p>
  
  <pre><code> AT+CUSD=1,"2A31303023" ,15
  </code></pre>
  
  <p>response</p>
  
  <pre><code> +CUSD: 2
  </code></pre>
  
  <p>I believe that the problem is about to be solved but what the response mean ?</p>