This message is only a warning and probably the log_fifo_size, the log_iw_size or the max-connections was changed from the original value.
A look on the config should show what was changed or even better a syslog debug archive can help to see the whole picture.
The max-connections and log-iw-size was changed from the default values. In the config log_iw_size/max_connections is 50, which is lower than syslog-ng's lowest value limit.
This warning is saying due to configuration set the log_iw_size became 50, but the lowest value allowed is 100, so syslog-ng automatically increased it.