Here is a reply i found which seems to explain it i'm just curious if anyone else has seen it and also the info might come in handy for others in future.
Event 1181 Active Directory could not delete the following column from the
database because it is being used by an index. This column was
previously used by the following attribute, which has been deleted.
The scenario is as follows:
An existing w2k3 forest, at w2k3 forest level;
Run R2 adprep to upgrade the schema etc;
dcpromo a R2 DC into the forest;
The events occur on the R2 DC, but not on other DCs.
Ideally, these abandoned columns should get removed. But Microsoft didn’t for
reason and report this event instead.
This is not a concern at all. The events are annoying.
This should be fixed in Windows Server 2008