This event simply indicates that the Application Virtualization Client log has been initialized (so now it is ready to record whatever messages the application needs to write in it). It typically indicates the restart of the client. The log file for the Application Virtualization (App-V) Client captures detailed information about operations and error conditions. You can use it when you are verifying functionality and when you are troubleshooting issues.
This event, in itself, is not a problem, but the fact that the client is restarted when it shouldn't be may be one of the consequences of a problem with the system. Look for other, more relevant events that may point to the actual source of the error. The specified log itself, may contain clues about what is happening.