What is the maximum SD memory card size that a Canon 510 and 520 Powershot can use?

Your camera only can use SD cards. The SDHC is a newer generation of SD cards, that need a different protocol you access the files. The newest version is the SDXC version.
SD cards never exceed 4 Gbyte. The SDHC never are bigger than 32 GD and the SDXC are over 32 GByte.
When you try to buy a SD card, the biggest you will find will be 2 GByte. I own 2 SD cards that have 4 GByte, but even I can't find them on the net any more.
The cards are from Platinum. But I even can't guaranty you the 4Gbyte will work in your camera.

Some firms used to bring out new firmware, as soon as the SDHC cards came out. I succeeded to update my TomTom to SDHC and the old thing now even accepts 16 GByte cards. But Canon did not offer an upgrade for the V550, so you stay stuck to the normal SD cards.

SD cards max out at 2GB. The S2 will not work with higher-capacity SDHC cards.

According to the specs on Canon's web site, the IXUS 700 works with SD cards, not SDHC cards. SD cards are limited to 2GB in size (there are rare 4GB SD cards, but they tend not to work in SD devices).

Of course, it's your call as to how definitive any manufacturer's web site touting their product might be.

You can use any size SD card. Just keep in mind that SD cards max out at 2GB; any larger cards are actually SDHC cards and will not work in the A510.

Te Camera can support the SD/SDHC Memory Card, MultiMediaCard, MMC Plus Card, HC MMC Plus Card upto 4GB.

Maybe it is having trouble with the size of the memory. Memory cards have grown enormously in capacity in the last couple of years, and even relatively new cameras may not be able to cope with the memory size of the newest cards. It is often difficult to find out the maximum capacity a camera will use, as today's memory cards are much larger that those available when the manual for the camera was written.

SD and SDHC cards fit the same slots, but many cameras won't work with the SDHC (high capacity) cards. SDHC is not backwards compatible.

you need an sd card and you should be able to put in at least 2gb card maybe more. any band of sd card is fine but i suggest sandisk they are pretty good

Check to see if your 16GB card is an SDHC card. If it is, your camera is not compatible with SDHC. (The SDHC protocol was developed after the SD300 came out in 2004).

I am not sure, but I think it is 16GB maximum

Buy a high speed 2G SD card(video eats alot of memory so go to the 2GB). Enjoy your camera.