Script level upgrade for database ‘master’ failed because upgrade step ‘u_tables.sql’ encountered error 25641, state 0, severity 16. This is a serious error condition which might interfere with regular operation and the database will be taken offline. If the error happened during upgrade of the ‘master’ database, it will prevent the entire SQL Server instance from starting. Examine the previous errorlog entries for errors, take the appropriate corrective actions and re-start the database so that the script upgrade steps run to completion.

Script level upgrade for database ‘master’ failed because upgrade step ‘u_tables.sql’ encountered error 25641, state 0, severity 16. This is a serious error condition which might interfere with regular operation and the database will be taken offline. If the error happened during upgrade of the ‘master’ database, it will prevent the entire SQL Server instance from starting. Examine the previous errorlog entries for errors, take the appropriate corrective actions and re-start the database so that the script upgrade steps run to completion.

Try this Solution : 

Nothing could be found in SQL Error logs.Check the service account of SQL Server, find out whether it has enough permissions to run SQLServer. If you are not able to change the Service acccounts permissions immediately and wants to come out of this Service Pack Installtion errors.  Change Service account for SQL Server to Local System. SQL Server DB Engine Service will be started and the build number will be updated too. Can revert your SQL Servers Service account back to Original from Local System.