Hello, I`ve bought a 4GB memory SDHC memory card to my Canon powershot A 430 camera, and when i put it in my camera - it says memory card error. I tried to unlock it by the small button, but didin`t help. What should i do?

The SD200 works with SD cards. Your 4GB card is actually an SDHC card. While it fits into the slot, it is electronically incompatible and will not work in this camera. You need to use SD cards, 2GB and smaller.

There are several possible causes for "memory card locked", "memory card error", or "no memory card". The most common is trying to use a 4GB or higher SDHC card with an older camera made before SDHC format came out. Other causes include problems with the tiny slide switch on the side of the card, or the electrical contact switch internal to the camera. The problem may also arise from simple formatting problems if the card has never been formatted in the camera (note that this will also erase the card). Troubleshooting tips for this problem may be found at this link. And finally, if the cards that you've been using are 4GB SDHC, that's your problem.

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.

First, make sure your camera can accept SDHC cards. If the camera says the card is locked, move the slide switch on the side of the card.

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.

SDHC memory cards are relatively new, and are sadly compatible with only the newest model cameras. For your model camera, recommend a maximum 2GB standard SD card. Fortunately, these days a 2GB card is very inexpensive.