Hi, That is part of a vm debug message and is seen because the arduino buffer is overflowing with too many messages.

Let's continue this in your first thread where you discuss sending your own serial messages at the same time and on the same port that the debugger is using.

What you are trying to do is supported but we need to ensure that we aren't trying to sending a million messages at 16mhz. The arduino can't transmit the data fast enough and we get data loss. There are many ways to ensure this works but I will ask more questions in your first thread