I get this message INTERNAL ERROR: !U:\global\src\ObjectDbx\DB\IMP\src\dbsymblk.cpp@502: eInvalidIndex when I try to make a new layout in autocad 2000/2002. what should I do to resolve the problem. In autocad 2006 and later there is no error but unfortunately is important to continue working in autocad 2002 format.

Have you tried running the REPAIR option?

Yes I reinstalled autocad. I also tried to open the file in different pc. The file is quite big (100mb) and I think I mess it when I deleted some of my custom layouts.

If you corrupted your file so badly you can't open it and you continue to get this error then in all probability the file is "toast".Have you attempted to open the file on another computer running AutoCAD?

Your CAD file is 100mb??? For future projects, perhaps you could utilize blocks and xrefs to help keep the file size down.You said you can open the file in 2006, right? If so, run an AUDIT to find and fix errors and then save back to 2000 format?

Unfortunately I tried in autocad 2007: a) audit and purge and fixed errors and deleted the unnecessary, b) i tried copying the whole drawing-little by little layer by layer to a new one, c) I also converted dwg to dxf to dwg, but nothing made it work when i saved it in autocad 2002 at least for more than 2minutes before a new internal error appears. The file works fine -at least for now- in autocad 2006 and later, but my boss wants it for cost reasons to make it work in 2002 format... The problems is that I can't make a new layout without an internal error.Cad64 it is a drawing that is being worked for more than 5 years by the ''Water Company'' in order to create a concetrated map of an area of more than 5000sq meters... It has more than 161000 blocks, half of them include attributes, and 65000 lines and polylines. Sure, xref would work fine for the future. But the current old personnel still draws with pens and stencils...

If the drawing works fine in 2006 but not in 2002 maybe it is not a problem with the drawing per se.  Have you tried to REPAIR 2002?  That is NOT the same as doing an uninstall/reinstall.