I have some users getting this error. I checked the limits in ISPC3 and it shows unlimited users, is this setting elsewhere also? I could not find any other config files that have that setting.
That's not a setting in ISPConfig, this must be a global setting in pure-ftpd and pure-ftpd has such an option according to its manual (simultaneous connections limit). Which Linux distribution do you use?
From using Internet Search Engines, it could also be having only 24 ports in the passive port list. Each FTP session uses two ports, so 24 ports allows 12 connections. I just used the error message with Duckduckgo.
