Which server are you using and what were you trying to do when the error appeared?
I was trying to make the code for the channel streaming for my application, the error occurred when I clicked on the WebViewer's icon in the "Blocks" section.
Now, the error occurs every time I click on an icon in the "Screen1" section.
The "Built-in" section isn't affected by the error and works fine.
Does the problem persist if you refresh the page and open the project again?
Yes, it still persists.
The "Viewer" section of the "Designer" section doesn't show anything.