I was getting folloing error. I was able to resolve with increaing the size of SYSTEM tablespace.

Error in execution of OCI function OEXEC, OEXN:
ORA-00604: error occurred at recursive SQL level 1
ORA-01653: unable to extend table SYS.IDL_SB4$ by 13 in tablespace SYSTEM

I have few questions,
1)why am I getting error ora-00604?
2)what should be ideal size for a SYSTEM tablespace for oracle 8.1.6?
3)When IDL_SB4$ table is used?