The file sender needs to explode them for you. There is an AEC Explode ARX
file, but it does not work with R14.
A better option for you might be to download the appropriate Object Enabler
so that you can use the backgrounds you get, and then just add your own
entities to the drawing.
Or, get into an understanding with your files creator to keep things dumbed
down for LT's use.
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Dean Saadallah
http://www.pendean.com
LT Express Utilities
http://www.pendean.com/ltexpress
Expanded Links Pages
http://www.pendean.com/lt/links.htm
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