While testifying in court, you discover an error in the crime report. When the defense attorney questions you about this aspect of the report, should you admit the error?

Yes you should report an error to the crime report when you are asked about it.

When you are sworn in to testify, you are legally bound to tell the truth without regard for whose side it will benefit, otherwise you are committing perjury, or lying on the stand. If an error is noticed, and as a witness you are asked about it, it is your obligation to explain the error.