My pen drive copies files up to only 24MB whiles there is much free space on it. My computer prompts of an I/O device error whenever the 24MB space is exceeded and it won't accept any data again. I tried it on other PCs and it did the same thing.When I formatted, there was a 4kb used space indicated.How can fix this problem. I suspect there are bad clusters on the pen drive. The size is 512MB from Sony.

Folikumah Makafui, March 2006

My guess is you have been sold a fake pendrive. There are more fake pendrives with Sony written on them than there are proper sony ones. If you bought it on the net, from Ebay, from a market, whilst abroad, from Hong Kong / Taiwan etc etc then it will be fake.
I would suggest making a formal complaint about the seller, as this is a major cause of fraud.

JRA, May 2006