If you run Wing FTP Server on Solaris, and you have hundreds of clients connected to your server, maybe you will encounter error message like "550 Can't access file." or "Cannot open file...". Because on the Solaris operating system, One process has the limitation for the number of open files(includes socket resource) restricted to 256 by default.
The easiest solution is: edit the file "/etc/profile", add the following lines into it:
ulimit -n 40960
Then restart your server, everything will be OK.