You could do this natively on Linux or Solaris with syslog-ng, or if you want a Windows-based solution you could export your Linux/Solaris syslogs to Solarwinds Kiwi Syslog server, and configure it to alert on arbitrary text patters.
Use the Linux Keyword File Monitor Template.
This template will SSH to the server and hit the log file in question looking for a keyword or phrase. When found the App monitor goes critical, and you can build an alert to trigger on this. There are a few more templates out there like this have have some variants in the Content Exchange section of the forum. Just search for Linux, Unix, Solaris Keyword Monitoring.
You might have to change some syntax up across different flavors of Linux and Unix OS, but the script is easy to manipulate and tweak if needed.