When VMware release ESXi 5.0 Update 1 the auto start manager broke which was first discovered and discussed on the communities and later on in an official blog post. VMware now released a new patch which resolves this issue. The new patch also fixes some other bugs and security issues.
Installing the patch does require a reboot of the host before it works again. If you have ESXi 5.0 Update 1 installed I suggest you update as soon as possible and benefit from autostart.