The error message "No connection established" typically occurs in the context of software development, particularly when using the Arduino IDE or working with ESP8266 boards. It indicates that there is an issue establishing a connection between the software and the hardware.

There can be several reasons for this error, including:

1. Network connectivity issues: Ensure that your device is connected to the internet and that there are no network problems or firewall restrictions that could prevent the connection.

2. Incorrect board selection: Make sure you have selected the correct board in the Arduino IDE or the appropriate settings for your specific hardware.

3. Driver or firmware issues: Check if you have the necessary drivers installed for your hardware and if the firmware is up to date.

4. Library conflicts: Sometimes, conflicts between different libraries or outdated libraries can cause connection issues. Ensure that you are using the correct and updated libraries for your project.

5. Compilation errors: Review your code for any syntax errors or issues that could prevent the compilation process from completing successfully.

It is important to note that the specific cause of the "No connection established" error can vary depending on the context and the specific hardware and software setup. Troubleshooting steps may differ based on the situation.

If you are encountering this error, I recommend checking the documentation and forums specific to the hardware and software you are using. These resources often provide detailed troubleshooting steps and solutions for common issues.

An error message like "No connection established" during compilation can be frustrating! To help you troubleshoot, I need some more information:

1. What are you trying to compile? Is it a program written in a specific programming language, or something else?
2. What compiler or development environment are you using? Knowing the specific tools might help pinpoint the issue.
3. Are there any other details in the error message? Sometimes, compilation errors provide additional information about the specific problem.
4. Have you tried any troubleshooting steps already? If so, what were they, and what were the results?

The more information you can provide, the better I can assist you in resolving this error.

In the meantime, here are some general tips for troubleshooting "No connection established" errors:

1. Check your internet connection. If you're trying to compile something online, make sure you have a stable internet connection.
2. Verify your development environment settings. Ensure that your compiler or development environment is configured correctly for the program you're trying to build.
3. Look for documentation or troubleshooting guides. Most compilers and development environments have online documentation or troubleshooting guides that can help you diagnose and fix common errors.
4. Search online forums or communities. If you're still stuck, you can try searching online forums or communities for people who have encountered similar errors.

I hope this helps! Let me know if you have any further questions or need more specific assistance.