I’ve seen that message quite a bit, and in my experience, it usually comes down to either hardware issues or a corrupted IDE.
For example, if I accidentally miss a bracket in my code, the IDE sometimes throws a cascade of strange errors that appear to be related to its own internal code rather than mine. In such cases, I’ve found that simply reloading the IDE often clears things up and helps it point to the real issue.
I’ve also had USB cables fail after several successful uploads. Longer cables and USB hubs tend to make the problem worse. Swapping the cable or connecting directly to the PC usually helps.
All of this assumes you’ve selected the correct board and port in the IDE.
As a side note, I’ve often seen messages like resp=??, but haven’t yet found a good reference explaining what the codes actually mean, maybe someday I’ll stumble across a full list!