SQL Sentry periodically collects data from the SQL Agent log. If this file becomes too large, the overhead associated with simply reading the log can become problematic. To prevent this, SQL Sentry will automatically stop reading the log and begin generating this message if the log file size exceeds one megabyte.
The following error is generated continuously:
Unable to synchronize log file because it exceeds one megabyte -or- Unable to synchronize SQL Server Agent Log file because it exceeds 1 MB
This message indicates that we were unable to synchronize with your SQL Server because the size of the SQL Agent log file (SQLAGENT.OUT) exceeded 1MB in size. This generally indicates that there are errors being reported by SQL Agent that need to be addressed. This may also indicate that the option "include execution trace messages" is turned on under SQL Agent error log options.
Reading the sqlagent.out file will show the source of what is triggering the log file growth. Inspect this log file and resolve any errors being reported. Restarting SQL Agent will recycle this log file and temporarily fix the issue, but it will only be temporary if the problems reported by agent continue to occur. SQL Sentry also provides an option under SQL Server Connection settings to Auto-recycle large SQL Server Agent Logs.
See the User Guide for more information on this setting.
Note that if "include execution trace messages" is turned on under agent error log options, that will definitely cause the agent log to bloat.
Note that there are new status messages in SQL Server 2012 that will fill the log up quicker and also add clutter to the Event Manager calendar view. For more information, please see this post.