I was trying to add a scsi controller to a ESX box to use in a VM running on the box. The ESX operating system recognized the PCI-based Adaptec controller (it was on the HCL) but when I added the SCSI controller to the VM, it would not boot and displayed the following error:

Unable to open SCSI device 'vmfs/devices/genscsi/vmhba3:5:0:0'(scsi3:0):Could not find the file. Failed to configure scsi3.

The problem was that there was an extra “:0” at the end of the file name. I edited the .vmx file for the virtual machine and it worked! Note that also you need to edit with wordpad (not notepad) because of the construct of the .vmx file. [more]

edit vmx file
Edit ******.vmx (wordpad, etc...)

(Before)
scsi0:1.present = "true"
scsi0:1.deviceType = "scsi-passthru"
scsi0:1.fileName = "/vmfs/devices/genscsi/vmhba3:5:0:0"
scsi0:1.allowGuestConnectionControl = "false"

(After)
scsi0:1.present = "true"
scsi0:1.deviceType = "scsi-passthru"
scsi0:1.fileName = "/vmfs/devices/genscsi/vmhba3:5:0"
scsi0:1.allowGuestConnectionControl = "false"

I was able to find a solution in the following VMware Communities thread: http://communities.vmware.com/thread/199408