Clob is not suitable for use with the UNIQUE integrity constraint

Hi Whiz,
I got this error message when I try to run a query in the database. I do not understand where I went wrong. I tried to trap the root cause of this error but I cannot. Please guide me to resolve this error message. Is there any other method available to trap the error? Thanks a lot. Your help is great.

Warning
Query Error. Error content is as follows.Skip?
Execute error:-248
1’th line is not executed (error)
Error description:
The attribute domain “clob” is not suitable for use with the UNIQUE integrity constraint
