There's no way afaik on restarting the management agent, you may need to get to the DCUI (yellow screen) directly on the ESXi host to restart agent or issue a reboot if you can't remotely reboot the system.
=========================================================================
William Lam
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at:
Twitter: @lamw
VMware Code Central - Scripts/Sample code for Developers and Administrators
VMware Developer Comuunity
If you find this information useful, please award points for "correct" or "helpful".