Error when executing an interface: Update Existing Errors

Question

Hi Everybody,
It has been a while since I last wrote into the forum! And this time I am contacting you all, because I have gotten an error and I really do not know where the issue is right.
I am creating an interface, to pass data from one Oracle table to another.
I have created it, and executed the interface! So far so good, BUT then something happens!
I do get an error in a step called:
27 Integration - <MY_BEAUTIFUL_INTERFACE> - Update Existing Errors
I do recon that the error is on the update part, as it is not bringing anything on the set part! Should I modify something on my Interface! Yes I must, but really do not know what!!! I was thinking on playing with the execution modes, which I have already tried, but do not know quite well what to do next!
I do really appreciate your help and guidance, once more!!
Best regards.
P.S.: Please do not hesitate to contact me, if any further details are required.
Looking at the errors I got on the description tab:
/* DETECTION_STRATEGY = NOT_EXISTS */
update     <DB_INSTANCE>.<MY_BEAUTIFUL_TABLE_T> T
set      (
     ) =
          select     
          from     <DB_INSTANCE>.I$_<MY_BEAUTIFUL_TABLE_T> S
          where     T.<FIELD_A>     =S.<FIELD_A>
          and     T.<FIELD_B>     =S.<FIELD_B>
          and     T.<FIELD_C>     =S.LRP_CLASS_ID
where     (<FIELD_A>, <FIELD_B>, LRP_CLASS_ID)
     in     (
          select     <FIELD_A>,
               <FIELD_B>,
               LRP_CLASS_ID
          from     <DB_INSTANCE>.I$_<MY_BEAUTIFUL_TABLE_T>
          where     IND_UPDATE = 'U'
          )

Answer 1

J_ORCL wrote:
Well I am on the diagram tab, over my target datastore, and over the colums, but please apoligize me, but i am finding this option that you are telling me!
Once I click onto the column, a new window opens, but it is a mapping one, not a properties one. Is this the one you are mentioning?
Once you click onto any column you will find the following section ( on the same page )
Mapping
Executed On
Update
Target column
Data type
What I am interested in the Update panel .