The rule for coinbases on Verus, Zcash, and a number of other coins with zk-SNARKs, is that you must "shield" your coinbase transactions before you can use them, by sending them entirely to a z-address first, then back to a t-address. the Wallet has a shield all recent coinbases option, but you must make a private address (use legacy until Sapling activates) before you will see the option in the send screen. it is possible to send the entire amount to a z-address manually, but the easiest way to do it is by using the automatic shield coinbase option on the send screen.