DV
You need to uncheck all your notification settings and then just set it at one level only. The notification error comes from having duplicated notifications set. (I think)
The message in the event log is inserted every time the page cache is rebuilt. If you are seeing very frequent insertions of the event log, then your page cache is being rebuilt too often. There are two things that can cause this:
1) A match on the regex field of 'rebuild page index' with an incoming request
2) An application or application pool restart. This may be due to memory size limits or other IIS App Pool settings which is frequently restarting your application pool. Normally it will be surrounded by other 'app start' type messages if this is the case.
The message is informational, it's not a problem unless you are experiencing poor peformance. I'll look at an option to turn it off in a future release.