Hello, I have a customer that has givin me a AutoCAD file saved as a 2004 from a 2010. Every time i insert a block or try to get a distance between two object I get an error saying APX_ERROR:eNotThatKindofClass.
 
What is this? What does it do to the file? Is is something to worry about?
 
If I hold down the escape button after the error it goes away and will insert the block or what ever I was doing.
 
Thank you in advance for your help.

It is an "ARX" error. See if this could help:
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=4922

Yes, that helped.