Thank you for the replies and the connection to the extensive discussions on this subject. I have two computers a primary edit computer and a back up. The primary, W10 pro has VP 15 and 16 the back up W10 home, has VP 14, 15 and 16. I discovered that VP14 on the back up will write BD discs, but 15 and 16 will not on either computer. So; in spite of the suggested work around's is there a bug in VP 15 and 16 that causes the problem?
“Here is a little bit more. If you have VP14, rename the folder C:\Program Files\VEGAS\VEGAS Pro 15.0\bdmux to something like bdmux-vp15. Copy the same folder from VP14 over to VP15. The "you are not logged in as administrator" message will still appear unless you specifically run VP15 as administrator but the BD render will complete without error.”
Is there a bug in vp 15/16, .... Well, at this rate of repeat offending, three times!, assuming the above fix does fix it, it’s absolutely lazy programming.