Folks,I have a problem when trying to open a 7.28Mb 3D modelled AutoCad drawings. A message comes up saying 'Fatal Error: Unauthorised Handling Reading'I can open it in DWG TrueView OK but not in my AutoCad 2007 workspace.Any assistance is welcome

There is probably something within the dwg that your cpu can't handle, causing it to crash. I don't use 3D but maybe purge the dwg if you are able to so it gets rid of nested items etc. Give it a go anyway. Try also cleaning the dwg up a little getting rid of any layers you don't require and then select everything that you want to keep. Paste this into a new instance of autoCAD and save so that it overwrites the original file. This will then leave you with what you have selected minus unwanted layers. As you will have saved this dwg into a new instance of AutoCAD you will then be able to purge the dwg again :)
Maybe this is a bit of hassle but it works for me with the horrendously large files!