Hi, can you give a bit more detail about (precisely?)
-- what ISO you are using to install (ie, SME server iso named, ...... / obtained from ... where?)
-- what config you are using for the VM you are trying to install ?
I've installed SME / and more recently "ClearOS" (ie, the successor to SME server) as a VM Guest on Proxmox, and it never gives me any pain. I think I use a more or less vanilla setup, ie,
VirtIO HDD and NIC
Linux 'latest' as guest type
IDE-CDRom default to attach the ISO
and it just boots
if needed - maybe? - you are using a very old? ISO / SME installer? you could try IDE or different 'devices' for your NIC/HDD/CD and see if that helps.
Tim