While making photographs the message No memory space and in the upper right of the screen a blinking icon reminding of a battery appeared. I tried to reformat the memory stick according to the instructions, but this does not help.

Try unlocking the card, theres a tiny little switch on the side of the memory card. If you already knew this sorry, the simple answers are often the problem! If this is not the problem I sugest trying a new card, you may be able to take your Camera into the Shop and ask to try the memory card because then if the card does'nt work you know not to buy a new card. Then you'll know whether the problem is with the card or the camera, hopefully it was the simple lock on the side of the card. Hope I could help and Good Luck. These days people need a lot of luck working with computers and other temperamental equipment.

Yep, Johan is right. I had the same problem with my memory stick and a DSC-P73. Open SetUp, choose second option in root menu (stick), choose format OK even it says its already OK, the message appears that all current data on the stick will be erased. After choosing yes you can start taking pictures again.

Try to format the card (somewhere in setup) Other than that, I don't know. Maybee try someone elses card before replace. Also, look for possible objects/dirt between card and camera. Good luck!