In WS_FTP — and probably other FTP clients — you can decide what happens when a transfer fails by setting the retry options.
In WS_FTP 2006, open the Options screen (Tools > Options) and then choose ‘Transfers’ from the left-hand column. The first two options let you determine how many times to retry failed transfers and how long to wait between retries.
If you don’t want WS_FTP to retry failed transfers, just set the number of retries to zero.