Diagnosis
While trying to copy a matrix you have attempted to copy a matrix ontoitself which is redundantly reduntant.
Keep in mind that the key to matrix is the compensation modifier, thetable ID and the enddate, so changing just the beginning date will alsocause the error that the tables are the same.

Procedure
Check your source and target matrices and change one or the other. Bemore careful next time, as such copy functions can often be dangerous.