ORA-01741: illegal zero-length identifier
Here is some information on the error:
ORA-01741: illegal zero-length identifier
Cause: An attempt was made to use two double quotes ("") as an identifier. An identifier must be at least one character long.
Your query has nothing of the sort. This may be an interaction between ksh and Oracle. Or you may have used double quotes when you mean single quotes. Or, you may have oversimplified the query when you posted the question. Or another query may be the issue.
Here is a simple example of the error on SQL Fiddle.