Could you post this in a different community? Maybe PCB? CAM350 and Gerber may not be something that Calibre users will have much experience with. This "Design for Manufacturing" is really focused on IC's rather than PCB.
Thank you, I have now posted it in the PCB design forum
AAkula, when you compare the ipc netlist to your gerbers you will get three types of errors. One is a short. If you tie analog ground to digital ground through a small piece of copper, or a non-electrical drawn line, your netlist will show two distinct nets. Cam350 will create one net when it scans the gerbers because they are physically tied together. This will report as a short. Whenever I short two nets like this, I add a IPC Netcheck note on the fab drawing identifying the shorted net names and location. It is a simple matter then to remove the line in cam350 and regenerate the cam350 netlist. This will remove the error because the two cam350 nets will now match the ipc netlist. Also, I never modify my gerbers in cam350 and save them. All my errors get corrected back in the database.
The other two errors will be found copper that doesn't have a corresponding net in the ipc netlist and missing copper that has an ipc netlist. For missing copper, if you were using a Gerber 274D format file that is using an undefined d code aperture, for example, it is possible that the cam350 gerber file is missing something that should be in the final plot. In this case the error reports a netlist in the ipc netlist that does not have copper where it should be. One example may be an oddball trace width for controlled impedance. Your standard list may not have a 5.3 mil wide trace aperture, so there is nothing tying point A to point B. The found copper could be created by manually tying mounting holes together with a drawn line. Since drawn lines are not electical, they don't have a netlist so the connection will not be in the ipc netlist, but the cam350 created netlist would add one. This will generate the error that shows extra copper that doesn't have a corresponding netlist.