I have a Canon powershot A700. I took out the old

On an SD card there is a switch at the side which can be moved to protect the card contents (locked) or permit writing to the card (unlocked). Just move this to the unlocked position.

the reason you are getting the error message is because your camera is compatible with a maximum capacity of 2gb. try to have your sd card replaced to a 2gb instead.

Did you format the card in the camera before trying to use it?

Temporary solution is to take out the memory card from the camera and use the card reader to connect to the PC/laptop. Alternatively, use the MY Computer option and click on Canon PowerShot A700 icon.

I would like to ask what memory card seem to be locked. is this literal so you cannot pull it out ? If so then the memory card might have been inserted in the wrong position.

try formatting ur memory card sometimes after adding deleting pics it gets corrupted or becomes in such a format that is hard for a camera to show u , becoz sometimes u use ur memory card on card readers and then edit them there so they are unable to be read in camera try formatting the card temme if it helps

Check to see if you have a foreign substance on the contactor in the camera.

Yes, SDHC memory cards are compatible with the Canon Powershot A700, so that means you can use card with capacities over 2GB. You can also see the manual to verify this, Canon Powershot A700 Manual. On page 8, it says that SDHC memory cards are compatible.

Check:
1 - If you're on a shooting mode (not on a video mode);
2 - If you have enough power from batteries (maybe flash is necessary and power is not sufficient...);
3 - If memory card is in...
Try it...

use a sd memory card reader-no software-plug and play-make sure you don't have 2 folders in camera storing pics in different places-check in menus for folder numbers