Issue Description
AEC objects are custom objects used in applications like AutoCAD Architecture to represent items like doors, windows, walls, etc. When a file which originated in AutoCAD Architecture is brought into Archicad the blocks can come in as empty squares.
Solution
Please reach out to the party who provided you the DWG and ask them to open the file in their AutoCAD application. Then run one of the two commands below to export the DWG in a format that the AEC Objects are converted to standard blocks which Archicad and other CAD applications can read.
The -EXPORTTOAUTOCAD and AECTOACAD commands create a new file and explode all the proxy AEC objects into regular AutoCAD objects. The intelligence of the AEC objects is lost in the new file, but the former AEC objects can be modified.