One problem is that for some reason or another, lines and objects on a 2D drawing are on different Z-Axis Planes.  you can select a line and look at the properties and the "Start Z" will have a different value than the "End-Z". 

 

I was wondering if there if anyone knows of a LISP routine or command where you could select a group of line/objects and it would reset the Z-Axis values to Zero.

 

Thanks in Advance.

You may also use command MZ (Move just in Z) to move particular objects or even create their copy just in Z-axis (with COZ command). There are also many command which will help you out with finding out problems in drawings from Manufacturers, such as SLANTED command that search for lines that appear to be straight but are not.

 

Check it out, you won't regret :)