## 4. Troubleshooting

### **Errors for Uploading Codes**

- If messy icons are displayed on the matrix of the board after uploading code, check if any characters have been accidentally added or deleted. You may click “check”![Img](./media/A5457.png). But note that some are not errors, just warnings.

- If the code is with a library, check whether the library is uploaded to the board. See “**How Mu Import Library to Micro:bit**”. And then check if any characters have been accidentally added or deleted.

### **No Printings on REPL**

- After uploading code, click “REPL” ![Img](./media/A5530.png) and it prints nothing. In this case, we need to press the reset button on the back of micro:bit board. 


![Img](./media/A455.png)