I did exactly what Keil support had told in this site : http://www.keil.com/support/docs/2747.htm. But nothing happened, my program was still in trouble. The error was still "Can't Load Flash Programming Algorithm!" and "Can't Write to RAM for Flash Algorithms! Erase Failed!"
Thank you for your help and have a good day.
When that happens, even setting the right algorithm for flashing, you can solve that issue reprogramming the chip via a serial cable or you can go on uVision, menu 'Project'->'Options for target 'xxx''->Debug. In the ULINK settings, on "Download Options", set the "Download to flash" option. Download your program and clear that setting back.