hello,
For authentication DLP check (login, password) in AD but then it chacks DLP account, do if you have an issue with your DLP DB this may lead to this kind of message.
did you extend existing tablespaces or did you create a new one ?
For extend you could follow this procedure :
https://support.symantec.com/en_US/article.TECH220104.html
if you create a new one, it depends if it is related to DLP or to other application.
Try to connect to your DB with a DLP DB account and try this command
"select * from Protectuser;"
if you do not get any result, it means there is something wrong in your DB .
You may chack log files from DLP to see which "real" error you face during authentication process.
regards