My Powershot 450sd camera is not reading 4GB SDHC

I've checked out your Canon Powershot SD550, and this previously written answer definitely applies to you, Wendy:

The problem is that your camera is only compatible with SD cards, not SDHC cards. You bought a larger card for your older camera, not noticing that it was SDHC (or not knowing that it mattered). The new card doesn't work, not because it or the camera is broken, but because it's not compatible.

Cards up to 2Gb are generally SD.
Cards of 4Gb are generally SDHC.
Cards over 8Gb have to be SDHC.

(There are exceptions. Sometimes, manufacturers make 4Gb SDHC cards but some have errors; they disable half of the chip and sell it as 2Gb, but it's still SDHC. 4Gb cards are almost always SDHC because they're cheaper, but 4Gb SD cards do exist. They are so rare that I've even seen a guru on this site claim they don't. I did own one once, but it was very expensive and turned out to be so unreliable that I had to return it. I don't recommend looking for one, because of the problems.)

Your solution is to go find a 2Gb card, and be extra sure that it doesn't say "SDHC" on it.

The Canon A430 uses MMC and SD cards. While SDHC cards will fit into the slot they are electronically incompatible and will not work. You need to use SD cards, 2GB and smaller.

Many people are unaware that the newer SDHC format cannot be used with most older cameras. Your camera was manufactured well before the SDHC format came out. I'm sorry, but there's no way that a 4GB SDHC card will work with your camera, it just doesn't understand the new format of the card. The max size card that you can use with your camera is a standard 2GB SD card. More info may be found at this link.

The A430 works with MMC and SD cards. It will not work with SDHC cards. You need to use SD or MMC cards, 2GB and smaller.

There are several possible causes for memory card errors. Some include trying to use of a 4GB SDHC card with an older camera made before SDHC format came out. Others include problems with the switch on the side of the card, and the switch internal to the camera. Troubleshooting tips for this problem may be found at this link.

1. Try to format your memory card using a PC/Laptop.

2. Now, insert it in camera and check whether its working!

please rate this advice if it helps....tc! :)

I'm guessing you bought a new 4GB SDHC card. Although it looks exactly the same as a standard SD card, the format the card uses is very different. Unfortunately your camera was designed before the SDHC format came out. Sorry, but a SDHC card will not work with your camera.

You'll need to use standard SD cards (usually those 2GB or less). But if you really want to use a 4GB card, do a Google search for 4GB SD "non HC", with the non HC in quotes. Believe Transcend makes one.

I'm guessing that you bought a new 4GB SDHC card. Although it looks exactly the same as a standard SD card, the format the card uses is very different. Unfortunately your camera was designed before the SDHC format came out. Sorry, but a SDHC card will not work with your camera.

You'll need to use standard SD cards (usually those 2GB or less). But if you really want to use a 4GB card, do a Google search for 4GB SD "non HC", with the non HC in quotes. Believe Transcend makes one.

I'm guessing you bought a new 4GB SDHC card. Although it looks exactly the same as a standard SD card, the format the card uses is very different. Unfortunately your camera was designed before the SDHC format came out. Sorry, but a SDHC card will not work with your camera.
You'll need to use standard SD cards (usually those 2GB or less). But if you really want to use a 4GB card, do a Google search for 4GB SD "non HC", with the non HC in quotes. Believe Transcend makes one.

Apparently IXUS 55 is not compatible with a 4GB SD card. Use a 2GB and you would be fine.