Search400.com member Gary shares his blunder:  

Back in the early days of my IT career our small firm of four people did not have its own hardware, so we did all of our work at our client sites. At one point, we needed to reload all of our software on a customer’s System/36.  Knowing that we had faithfully backed up all of our software on a regular basis, we deleted all of our program libraries and tried to restore from the backup diskettes. We discovered that the diskettes did not contain any of our libraries, only the system library. We tried the previous set of backups. Same results. What we soon discovered was that the command we had been using “BACKUP xxxxxxxx” didn’t take any parameters and was used just to back up the system library. We finally found a set of backups from 6 months prior that contained our libraries. What saved us was the fact that since we didn’t have our own hardware, we always kept a current printed version of the compile listings. We recompiled all of the programs from the backup, printed the compile listings and then four people spent a full week comparing the two compiles for each program by laying them on top of each other at a window and bringing the source current. Needless to say, we never made that mistake again.  

Do you have a blunder to share?