With ESXi 3.5, the memory allocated to the VIM (host OS) can, sometime, be not proportional to the physical memory present on the system. So for some machine with 1 or 2 GB of RAM, you may have the following error “Admission Check failed for Memory Resource” while starting one VM.
In such case, decrease the quantity of RAM allocated to VIM, by opening your VI client then:
-click on tab “Configuration”
-click on “System Resource Allocation”
-click on node “VIM” then “Edit Settings”
-On the Memory Resources reservation, Enter Value 192MB (instead of 512MB by default)
This error may occured after an update of host Firmware.
At courtesy to Dave Mishchenko (http://communities.vmware.com/thread/140488;jsessionid=489E3D6A42D5F4E072A20C50F2666566?tstart=0)