Impact 128 MB SD Card and Pentax Optio S4i don't work!

During the thanksgiving weekend I purchased an Impact 128 MB secure digital memory card for my digital camera (Optio S4i) at Walmart, because the price was really low (U$15). My friend Vanessa also purchased two memory cards of the same brand.

When I tried the memory in my camera, it seemed to work ok, but I noticed that the camera was taking more time to record the pictures. But then after taking a few more pictures, the camera displayed a black screen with the following message:

“Memory card error”

Vanessa also tried her memory and both cards failed with the same error message.

I even tried to format the memory card with the camera and it failed to do so.

I want to try the memory with a different type of camera to see whether the problem is caused when using that type of memory with an Optio S4i, or if it is a problem with the cards.

I have another memory SanDisk and it has been working great for the last 6 months.