ADT In AutoCAD 2006 - Layer Issue

[omorah]

I cannot create a new layer, or change an existing layer when I open a drawing created in ADT (The ADT must be ADT 2006 or prior). When I create a new layer or change an existing layer, I get the error (Please see attached file) OR AutoCAD will automatically close.

However, if the same file is inserted as a block, I can create a new layer or rename the existing (ADT) layer name.