The OBSERVED "Network Errors;Miscellaneous" is a Websense category. The error occurs when WebSense performs a DNS lookup for the URL request and the IP address is unresolvable. Websense assigns the pseudo-category "Network Errors" to failed DNS lookups.
Please check if "restrict dns" setting is enabled on the ProxySG. Restricting DNS is generally incompatible with effective use of Websense, or at least with getting good filtering for the hostnames and domains that are restricted.