Summary: If you don't meet the minimum 4GB of RAM you may get this error.
I used to do a few custom ESXi VMs for my nested hosts, keep them there and modify them as needed.
Reason for that is the default settings are not of my particular liking. I don't let them have a 40GB disk - 1GB is more than fine for my lab. Likewise, I started my templates with the least amount of ram; in 5.0 and 5.1, that meant 2GB. 5.5 raised the minimum limit to 4GB, and told you very clearly about it! (felt like RTFM after that)
This will become important later.
I naively installed my first ESXi 6.0 GA host with 2GB of RAM, and ran into this
"Well WTH?" i thought. I googled around but there wasn't anything too clear for "no network adapters" in ESXi 6.0 GA or VMware Workstation. I assumed there had to be a mistake so I checked the settings. Workstation doesn't let you choose the NIC adapter, although you can edit the VMX file.
Checking the VMX files, one for 5.5 and 6.0 I could see the e1000 adapter clearly listed.
Then I took a step back, (RTFM echoed in my head), and I went to check what the requirements were for ESXi 6.0 and saw 4GB ram - I thought, well let's get that fixed although there wasn't an error like in 5.5. Lo and behold, the installer now worked and I was able to install without any other problems.
So, there's a "gotcha" there, and that's what this blog is about :)