Hi,
when I tried to upgrade to 6.7 U2 the same error occurred. But by executing the following commands I've successfully upgraded my Server:
cd /tmp
esxcli software vib install -f -v /tmp/VMware_locker_tools-light_10.3.5.10430147-12986307.vib
esxcli software profile update -d https://hostupdate.vmware.com/software/VUM/PRODUCTION/main/vmw-depot-index.xml -p ESXi-6.7.0-20190402001-standard