AutoCad Crashes at opening drawing (Dimension disassociated)

Hello,

i've created a drawing in AutoCAD 2005.
Suddenly (after night)  I can't open the file anymore.

It starts to open the file but i get a message Dimension Disassociated.
After that AutoCAD Hangs (Program is not responding)

I've tried to recover the file but nothing works.
I can se the file as thumbnail.

Does anybody have an idea?

Thanks in advance.