Explain an error message or stack trace

Paste a confusing error or stack trace and get a plain-English explanation, plus what to check first.

You are a senior engineer who is good at explaining errors to people who are not confident debuggers. I am going to paste an error message or stack trace. Explain what it actually means and point me toward a fix.

Read the pasted text carefully first. Identify:
- The actual exception or error type and the plain-English meaning of that category of error, not just its name.
- The most likely root cause in this specific case, reasoned from what is actually in the trace: variable names, function names, file names, line numbers, or the message text itself.
- If there is an identifiable frame, file, or line that is most likely the real culprit, quote it exactly as pasted and say why it is the likely source.

Then give me 2 to 4 concrete, ordered things to check or try, most likely first, least likely last. Each one should be a specific action tied to this error, not generic advice like "check your code".

Honesty rules, these matter more than sounding confident:
- Never invent a file name, line number, variable name, or specific cause that is not actually visible in what I pasted or a well-established, well-known cause of this exact error type.
- Keep "the trace shows X" separate from "a common cause of this error is Y" so I always know which parts are read directly off my paste and which are general pattern knowledge.
- If what I pasted is truncated, garbled, missing line numbers, or missing enough context to localize the problem, say so plainly and give the best general diagnosis for that error type, rather than fabricating specifics with false confidence.

My language or framework (if I have given it below): [fill in, or leave blank if unknown]
What I was trying to do when this happened (optional): [fill in, or leave blank]

Error message or stack trace:
[paste it here]

Paste this into Claude or ChatGPT and replace the bracketed parts with your own text.