Now I want to Save some information to the SD memory.
When I download the ReadWrite file from the SD memory library, it's working properly.
Now, when I integrate the SD memory code, with the keypad and a barcode scanner code, the SD card does not get initialised. "Initializing SD card...initialization failed!
"
The SD card's SS pin is connected to pin 4 of your Arduino board. So try connecting the keypad to a pin other than pin 4 and update your code accordingly. You should also be sure your code uses SD.begin(4) to set pin 4 as the SD card SS pin. If that doesn't solve your problem then you probably need to provide some information on what sort of hardware you have connected for the barcode scanner part of the project.
You will also notice that pin 7 of your Arduino board is used for "handshake" with the shield, which is likely why the original problem was solved when you changed the keypad connection from pin 7 to pin 9.
So you have a configuration that works one that does not. There is something different between the two configurations that caused the breakage.
The key to troubleshooting is to rule out as many possible causes of that breakage as possible. Once you can determine the cause of the problem you're 90% of the way to fixing it.
You said:
FutureEngineer:
when I integrate the SD memory code, with the keypad and a barcode scanner code, the SD card does not get initialised.
So you made a bunch of changes all at once, thus you don't know which of those changes caused the breakage. This is why it's very important to do incremental development in small steps, testing after each one. It might seem slower at first but in the end it's much faster and less frustrating.