530 Sorry, the maximum number of clients (10)

…for this user are already connected.

Why me this error when I log in via ftp?
Is it limits the size of files for upload?

Are you logged into FTP multiple times at once? My FTP client can do uploads in parallel, but each one takes one FTP connection. If you have your FTP client set to run more than 10 uploads at once before it goes to the queue, you’ll get this.

I have mine set for 3, which is enough, considering I’m just using my one connection.