This error occurs when symbols from separate units are combined into a common namespace, and the same symbol name is in both units. In previous versions of Delphi, these units may have compiled without error, because symbol scope was defined by the unit alone. In RAD Studio, units must be inserted into namespaces when generating the IL metadata. This may cause separate units to be be combined into a single namespace. 

To resolve this problem, you may wish to rename one of the symbols in the two units, alias one of the symbols to the other, or change the unit names so that they do not contribute to the same namespace.