Failed to create new pty

Operating system: FreeBSD 7.0, 6.3

Error message was: Failed to create new PTY

I absolutely don't know how this problem can be reproduced. It happend to me while I was backuping to tar format, but it disappeared somehow. I was trying to restart webmin, to clean temp files and finally I've rebooted machine. Nothing helped. But now it works. This occured in webmin.

I had same problem with my virtualmin installation.
Same problem while I was backuping all virtual servers.

I've read that someone has the same problem during installation of perl modules. Only one idea - it happens only on FreeBSD.