I tried everything you asked, lock, send, unlock before send...
Error: Missing private memo key for sender: 1.2.xxxxx
g</<.value/<@https://bitshares.openledger.info/graphene_ui/app.js:51:10699
z/</l@https://bitshares.openledger.info/graphene_ui/app.js:2:153
z/<@https://bitshares.openledger.info/graphene_ui/app.js:2:288
d@https://bitshares.openledger.info/graphene_ui/app.js:2:2704