During duplicate resolution, records that were created with no Created or Modified date will show the following error when performing duplicate checking against them:
This can happen with legacy records that were loaded into the system directly through database insert. In order to resolve this, ensure the columns CREATED and MODIFIED on the MIXTURES TABLE have a value.
Classic Registration does not throw an error in this situation, records that were OK during duplicate resolution on Classic Reg may throw this error now on Web Registration.