Now that you installed the desktop wallet of coinomi, have you tried sending the DGB to any wallet you owned? You can try their
official wallet (hit the download button) mobile or desktop, it's also available on edge with segwit support.
Heh, I missed that he had already installed the desktop client.
dutchlincoln has not been online in a couple of days, but not knowing how many transactions the coins came in on I am guessing that he might have hit a limit on transaction size / max number of coins per transaction.
Coinomi does not always give a nice error when that happens. I had a similar issue with defcoin a few summers ago when I was giving them away a defcoin. I could nor do a transaction for 100k coins but 4 x 25k worked fine....
-Dave