I have done what I should have done in the first place which is try FTPing a zero length file to my ISP using a different client. I have tried FileZilla and it behaves the same as WinSCP, in that re-sending a zero length file does not update the timestamp on the file on the server. I suppose that means that it is an issue with my ISP's FTP server. I presume that this is not a common problem or you would have encountered it before. I will contact my ISP.
Thanks for your help.
Colin

I'm not able to reproduce the problem.
Can you give me simple description of steps to reproduce it?
E.g. Does the problem occur if you take single empty file and upload it to the FTP server?

I am using synchronize (FTP) to update my website from my PC and it works very well except except that zero length files are transferred every time I synch. This is caused by the fact that the timestamp of the zero length remote file is not updated even though the file is being transferred. Is this something to do with WinSCP (4.1.0) or is it likely to be something I have to take up with my ISP? If it is a problem with my ISP is there any way round the problem using a feature of WinSCP? I can get round it manually be deleting the files on the server but there are a lot of them so this will be a bit tedious.
Thanks,
Colin