The Graph Log utility is slow. There seems to be a high number of connections to the mail-server from a specified IP How do I find out what a selected account is doing?
To solve this error use the Purge Logs utility to delete logs older than X logs( X being the timespan you specify). This will make the system load the logs faster, and increase performance.
You can edit the SMTP/POP3/IMAP settings through the WebAdmin, so to reduce the number of connections per IP.
You can use the Search Logs feature, by specifying the account type and log-files to search.