Debugging ProxMox Install on some Mainboards
Boot typing debug at the boot prompt - this will give you a shell a various places - simple press Ctrl-D to continue the installer. After the installer shows the error, press abort to get a console.
Then check if the HD device is detected and how it is named:
# ls /sys/block/
What is the content of
# cat /sys/block/sd<X>/removable
Maybe it is marked as removable drive?
#ls /sys/block hdc ram0 ram10 ram12 ram14 ram2 ram4 ram6 ram8 ram1 ram11 ram13 ram15 ram3 ram5 ram7 ram9 sda sdb
#cat /sys/block/sd[ab]/removable 1 1