(3).7z.003 -

: This happens because the "header" (the table of contents) is usually stored in the .001 file.

: Ensure you have every numbered file in the set (e.g., (3).7z.001 , (3).7z.002 , and (3).7z.003 ). (3).7z.003

Are you getting a specific when trying to open it? What operating system are you using (Windows, Mac, etc.)? : This happens because the "header" (the table