The agent log is created at the agent start up, please double check if your agent is really started. A common problem, for the agent not being started, is the missing masthead in the folder /etc/opt/BESClient. In such case you should get the following error:
root@nc1474133 # ./besclient start
Starting BigFix: BESClient
Missing masthead /etc/opt/BESClient/actionsite.afxm.
Is the Solaris architecture SPARC or Intel ?