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I want to build a project, but I will receive the prompt ：The target "Build" does not exist in the project.If I use "Rebuild", the "Build" in the prompt will be replaced by "Rebuild". The same is true of "clean"。
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(201.6, 57.00000000000001%, 29%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EMY%3C/text%3E%3C/svg%3E)
Could you provide steps to reproduce the problem?
I I can't find where to submit the screenshot
I am using TwinCAT to write code, and the solution includes two projects.MainThread project will encounter errors in the description during the Build process, while the TCPServer project will not. As shown in the figure below. 
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(256, 32%, 34%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EMT%3C/text%3E%3C/svg%3E)
Please show us your project setup, screenshots, etc. What you've given us is not sufficient to diagnose anything. As far as we know you just opened a .cpp file and tried to compile it which won't work. If you're running a command line manually then provide us that command line. The more information you provide us the far quicker we can help.
I am using TwinCAT to write code, and the solution includes two projects.MainThread project will encounter errors in the description during the Build process, while the TCPServer project will not. As shown in the figure below.
This is a screenshot of my project settings
Given you're using a third party tool that seems to control builds I would suspect the issue is there. The screenshots you showed are not of 2 projects but a single, TwinCAT project. How it breaks up and compiles things is a question for the devs who wrote it.
The only thing I see off in the screenshot you gave is that the platform toolset you have selected isn't valid for your machine (notice the not installed). But since this is part of a third party extension I don't know what you should be using there. Perhaps just change the platform toolset to something that is installed. But it isn't clear whether this applies to both projects or not.
Ultimately I think you need to contact the TwinCAT devs for this issue as it isn't directly related to the C++ build system since that system is being called in a custom manner by the extension I'd wager.