This error message means that the disk with Agent's storage has ran out of space and the Agent cannot continue recording the log.
It's advisable to clear space or add more space to the disk on the disk ASAP. The error shall automatically clear itself after more free space is available.
See here to learn where agents store the logs and other service data depending on the operating system. Remove some of the unnecessary files from the disk or partition. It's also possible to free up space occupied by Resilio Connect by deleting some of its files, see here for more details.
Error code SE_LOGFILE_ERROR