Is the Pentax Optio S4i compatible with newer memory cards? When I put my new SanDisk Ultra 4BG SD card in, the camera turns on, but the screen stays black for a few minutes, then gives the message "Memory Card Error". My old SanDisk 1BG card works fine.

There are several possible causes for "memory card locked", "memory card error", or "no memory card". The most common cause is having the tiny slide switch on the side of the card in the wrong position. The second most common is trying to use a 4GB or higher SDHC card with an older camera made before SDHC format came out. There are also other common causes if the above didn't help, with troubleshooting steps for this problem listed here.

No. The S40 works with SD cards, not with SDHC cards. You have to use SD cards, 2GB and smaller.

Are you formatting the camera or the memory card? You should do both. Also, make sure of the position of the slide switch on the side of the card.

You need to format a new card in the camera.

here is a list of compatable memory cards
http://www.4allmemory.com/index.cfm?fuseaction=search.memorySearch&model_id=42425
.. any SD or MMC card should work up to 4 gb ... so your 2gb should be ok .. i suspect that it may be damaged .. you can try formatting it in a USB card reader if you have one on your computer .. some laptops have the SD slot built in .. there was some compatability issues with memory cards for older cameras but there shouldnt be any with such a new machine .. make sure the contacts are clean and the "protect" switch (if any) is in the unprotected mode .. when you format the card it may take several minutes so give it time .. if you are going to take movies then its better to use a "high speed" SD card .. like the 133x mentioned in the above URL .. slow memory may cause missed frames or 15 fps instead of 30 fps record rates.. .
the specs on your camera do show SD and MMC compatability .but they dont show any brand preference .. .

Does the camera work with any other card? Was the card formatted in the camera? Some cards from some manufacturers just don't work in some cameras.

It will not work with any "sdhc"

The E10 works with 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.

I don't know for sure, but it sounds like it could be a memory card problem. Have you tried it with another card or no card at all? My S4i froze up completely from a bad sd card. The green power button would light up, but nothing else would happen. Pentax recommends Lexar or Panasonic sd cards from what I have heard. My new Lexar card hasn't had any issues.

I have a friend who had an s4i with a 1gig sd card with no problems.