Steve,
the lines in your block have been drawn on layer C. Thus they get
turned off when layer C gets turned off. Your block could have had
many lines on *different* layers and each part of the block would
react to their layer visibility. To turn off a block with all lines
disappearing, you need to FREEZE the insertion layer, not turn it OFF.
Dietmar Rudolph
President, CR/LF GmbH, http://www.crlf.de
Vice-President Europe, CADLock, Inc. http://www.cadlock.com
Member of the Autodesk Discussion Forum Moderator Program
Author, "Mastering AutoCAD 2000 Objects", http://www.crlf.de/Verlag/PublishingServices.html