Question:  I am seeing this ORA-01691 error and my database is hanging:

ORA-01691: unable to extend lob segment WM65NAIP.SYS_LOB0003$$ by 128 in tablespace NAIP65_DATA
ORA-01691: unable to extend lob segment WM65NAIP.SYS_LOB003$$ by 1024 in tablespace NAIP65_DATA

How do I correct the ORA-01691 error?

Answer:  The oerr utility  shows the cause and action for the ORA-01691:

ORA-01691: unable to extend lob segment %s.%s by %s in tablespace %s  

Cause: Failed to allocate an extent of the required number of blocks for LOB segment in the tablespace indicated.  

Action: Use ALTER TABLESPACE ADD DATAFILE statement to add one or more files to the tablespace indicated.

In this case of an ORA-01691 error, the solution is to identify the name of the tablespace associated with the LOB segment and add space to the tablespace using the "alter tablespace xxx add datafile yyy size zzz" syntax:

alter tablespace
   NAIP65_DATA
add datafile
   '/u01/app/oracle/ . . . /xxx.dbf
size 10G;

Note:  Sometime the ORA-01691 error is truncated to ORA-1691:

ORA-1691: unable to extend lobsegment WM65NAIP.SYS_LOB0003$$ by 128 in tablespace NAIP65_DATA
ORA-1691: unable to extend lobsegment WM65NAIP.SYS_LOB003$$ by 1024 in tablespace NAIP65_DATA