Using files originally created by 2010 in 2009

so basically i normally use autocad 2009. early this week i had to use 2010 working on the same file. im now back to 2009 and even though ive saved it as a 2007 file it wont let me paste anything into the drawing. it says that it is invalid. is there a way around this at all?
ive attached a screenshot of the message that appears when loading up also.
any help with this would be great.

But you're not using "AutoCAD". Civil3D was involved, and even if you are not doing any civil3d type work, there are still C3d objects embedded in the drawing database. And Civil 3D has NEVER been backwards compatible.

To resolve this, type in -AECEXPORTTOAUTOCAD at the command line, and follow the prompts to create a new file with nothing but vanilla drawing entities.

Note that runnng "Civil 3D as AutoCAD" is still running Civil3D. It's a different build of the base package, and will create c3d dictionary object in every drawing it's used on.

yeah thats done the trick nicely.

thankyou cadtag.