Strange problem... Filenames must be more than 6 characters?

I have been using Smart FTP for a while now and have not really had any problems with it. until now that is.

I can upload files no problem as long as their file name is long enough. the problems come when the filename is less than 6 characters before the file extension. Has anybody else ever had this problem, and if so, how did you fix it? i am having to rename files, upload them, and then rename them back to their original names which makes uploading very time consuming .

If anybody could help me out here it would be much appreciated,

Thanks.