AutoCAD [and therefore ADT] will use the first ACAD.pgp file it finds. Could there have been a change to the search paths [additional folders or changed order] between now and the time when these worked? Could a rogue copy of an ACAD.pgp file - without the desired aliases defined - been copied to a folder earlier in the search path than the out-of-the-box version? [The folder in which the drawing you are editing is also part of the search path - is there an ACAD.pgp file there?] Could the out-of-the-box ACAD.pgp file have been edited or overwritten in its folder?
Autodesk Discussion Group Facilitator
Using ADT 2004 at work; access to 2005, 2006 & 2007 at home