Expert: J. B. Borge - 12/14/2007

Question
Sir iam using autocad 2006 earlier i use to use autocad 2004 even after changing to 2006 the files were opening properly but when i installed autocad 2008 not all the files some files started giving message called drawing file is not valid can u pls solve the problem for me

Answer
Murphy, the only time i get this error is when you're opening a drawing (new version) from older Autocad release. Ensure this is not the case. Additionally, install most current service packs see if this addresses the problem.
You can also try opening the Autocad drawings (ones that rendering the error msgs) in Notepad. This way, you can verify which release of Autocad the dwg was generated from. You should see a tag in the beginning such as:
AC1015 = for ACAD '00-'02 Rel.
AC1018 = for ACAD '04-'06 Rel.
AC1021 = for ACAD '07/'08 Rel.