An error message when I put the memory card in

If it's an older camera it may not accept a card of a size above certain limits -- see camera spec or manual and see if it mentions a size of card -- that may have been the largest made at the time the camera was released..

Problem can also occur if a card of any size has previously been used in another camera or device. In that case you need to reformat the card in the Canon.

The thing is that I bougth this camera on Ebay iand it came working just fine, after a few minutes, when I opened the case to change the memory card (Compact Flash), stoped working. So, I'm not sure if the problem is the card or the camera because it's not when I put the card in, the problem occurs when I open the case to insert the card, the camera turns off, and then after inserting the card, when I close the thing and try to turn the camera back on, it says (ERROR). PLEASE HELP ME!!!!

Did you switch off the camera before meoving the card. If not the card may be corrupt.

I think I'd take it to a camera retailer and ask them to test with a new CF card and see what happens.