A AutoDesk tem algumas sugestões de reparo aqui. link
If neither of the above options allow you to open the DWG, move on to the next set of steps. These steps can be tried one at a time. Be sure to stop and try to open the file after each one. If the file opens, there is no need to continue to the rest of the steps.
Open a blank DWG and run the RECOVER command. Select the problematic file. AutoCAD will attempt to recover the file and open it.
Open a blank DWG and run the RECOVERALL command. Select the problematic file. AutoCAD will attempt to recover the file and open it.
Open a blank DWG and run the INSERT command. Select the problematic file and see if it will insert. If it does, then run EXPLODE and select the inserted block. Run AUDIT and PURGE commands, and then use SAVEAS to create a new DWG.
Look in the same directory where the DWG resides and see if there is a BAK file of the same name. If so, rename the BAK extension to DWG and see if the file can then be opened.
Look in C:\Windows\Temp for files with an SV$ extension. If any exist with a similar name to the corrupted DWG file, then rename the extension to DWG and see if it can then be opened.
Go to your backup system and restore the file from a time before it became corrupted.
Nota: Eu sou novo aqui. Se eu deveria fazer links e citações de maneira diferente, deixe-me saber o que preciso mudar.