ORA-01691 although lot of space available in the tablespace

  Hi

we are getting the following error on one of the tablespace (IMG_DATA)


ORA-01691: unable to extend lob segment IMAGING.SYS_LOB0000417108C00002$$ by 5 in tablespace IMG_DATA


although we have about 8 GB free space available in the tablespace


select tablespace_name,sum(bytes)/1024/1024/1024 AXCS,
sum(maxbytes)/1024/1024/1024 AXMS,
(sum(maxbytes)/1024/1024/1024)-(sum(bytes)/1024/1024/1024) AXFS,
((sum(bytes)/1024/1024/1024)/(sum(maxbytes)/1024/1024/1024))*100 AXPU
from dba_Data_files
where autoextensible='YES' and tablespace_name='IMG_DATA'
group by tablespace_name
order by 1;



                                   CURRENT         MAX        FREE
                                     SPACE       SPACE       SPACE
                                     USAGE      USABLE   AVAILABLE PERCENT
TABLESPACE_NAME                         GB          GB          GB    USED
------------------------------ ----------- ----------- ----------- -------
IMG_DATA                             33.21       41.40        8.19   80.22