Acronis True Image 2010 will no longer backup

I back up the C drive completely every so many months. Acronis is now refusing to back up after numerous attempts and computer restarts. Either Acronis causes the computer to blue screen (which it never does in other circumstances) or Acronis reaches an error and stops. According to the log, that error appears always to be failing to read data from the disk, from the same particular numbered sector 24,058,374.

Version Acronis True Image Home 2010
System is Windows Vista Home Premium SP2 32 bit
4Gb Ram, 2.4Ghz processor, the C drive partition is 240Gb of which 150Gb is in use
Plenty of space on the portable hard drive to which I am backing up
Never had any problems with Acronis before

I should be most grateful for any suggestions
Thank you