Upload?

Ive been having this problem since day one,

I connect to any FTP server, works all fine, i can browse though the files
I can download the files onto my computer easily,
But I Can't seem to upload?
Every time I do the connection rather times out, or transfers the file with nothing in it..

I've tried to do this through internet explorer aswel and the same things happen, it takes ages to transfer the file and then the file appears with nothing in it..

If anyone could help id be very greatful!

Thanks, Mol3