Undefined control sequence in .bbl file during bibliography rendering

A LaTeX project utilizing BibTeX for bibliography management generates an Undefined control sequence error during the final compilation pass. This occurs after the pdflatex → bibtex → pdflatex → pdflatex sequence has been executed.

The error originates from the .bbl file, which is automatically generated by the BibTeX engine from the .bib source. This suggests a mismatch between the formatting commands injected into the intermediate .bbl file by the chosen bibliography style (.bst) and the definitions available in the current document class or loaded packages.

• What causes the BibTeX engine to insert control sequences that the LaTeX compiler cannot resolve?
• How can the specific incompatible command be identified within the generated .bbl file without manually editing the file?