ORA-65086: cannot open/close the pluggable database

SYS@CDB>startup
ORACLE instance started.

Total System Global Area 1073741824 bytes
Fixed Size    2932632 bytes
Variable Size  633340008 bytes
Database Buffers  432013312 bytes
Redo Buffers    5455872 bytes
Database mounted.
Database opened.
SYS@CDB>show pdbs

    CON_ID CON_NAME  OPEN MODE  RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED  READ ONLY  NO
3 PDB1  READ WRITE NO
4 PDB2  MOUNTED
5 NCDB  MOUNTED
SYS@CDB>alter pluggable database ncdb open;
alter pluggable database ncdb open
*
ERROR at line 1:
ORA-65086: cannot open/close the pluggable database


SYS@CDB>! oerr ora 65086
65086, 00000, "cannot open/close the pluggable database"
// *Cause:  The pluggable database has been unplugged.
// *Action: The pluggable database can only be dropped.
//

SYS@CDB>drop pluggable database ncdb;

Pluggable database dropped.

SYS@CDB>create pluggable database ncdb using '/home/oracle/sales/nvdb.xml' nocopy tempfile reuse;

Pluggable database created.

SYS@CDB>alter pluggable database ncdb open;

Pluggable database altered.

SYS@CDB>