Sorry I've corrected my previous message it is nadm issues.
Could the error message be "mdadm"? I see you have a USB stick in your system configuration. If you are using it for your OS, I know that some fresh installs of OMV 4 fail when installing from a USB device to a USB device. This is apparently a Debian installer thing, and not an error with OMV. I have see in my case, the error is an "mdadm" error for "missing array", even though the systems I've installed on had no RAID array.
I know that sometimes, as @gderf mentions, you'll get a series of errors and eventually the system boots normally. But, I've experienced myself that some configurations that it won't boot at all.
One thing to try (and has worked for me), is as noted above: reinstall OMV 4 with all the data disks disconnected and only the installation USB and your USB drive for the operating system inserted. But, after the install is done, remove the installation USB AND leave the other disks disconnected during the first reboot. Boot with just the OS USB flash drive inserted.
When the GRUB menu displays, there will be a message at the bottom of the screen stating, among other things, to hit the "e" key, to interrupt the boot sequence and allow you to edit boot parameters. Hit the "e" key and the edit screen will come up.
From the editing screen look for the line for "linux", which will probably indicate the boot drive as /dev/sdb or /dev/sdb1 or similar, rather than a long UUID string (which is preferred). If the listed drive isn't "sda" (or sda1 or similar drive ID), change it to "sda", or "sda1" etc. and continue the boot process (the F10 key does that I believe). If it does list a UUID, then you probably have a different error all together.
If your system does finish booting, you can then log in through the Web UI, and apply the updates available in the "Update Management" tab. One (or more) the the updates will trigger an update to the grub configuration and that update should also permanently fix the issue from the installation. Once the updates are complete, you can shutdown, connect your data disks, and try booting again.
Details on this issue (if it is this issue in your case) and information on how to fix it manually with manual edits to the configuration files, are in this Forum string: mdadm-no-arrays-found-in-config-file-or-automatically. But, since some time has passed and there's now an update to OMV (or the underlying Debian) that happens to fix the issue automatically (at least for me) through the Web UI, I've found that easier.