When I try to run a MOPAC minimization, I get the following error: output file doesn't exist! error: Cannot locate output file!
You need to update your MOPAC application.
1) Run Chem3D
2) Select the Menu option: Calculations / Mopac Interface / Check for Update This option will indicate that an update is available and open a browser, on the Chem3D / MOPAC 2007 update page: http://openmopac.net/Download_CS_MOPAC_Executable.html
On this page there is a link to a zip file containing the newest available mopac2007ultra.exe.
i) Click on "Download MOPAC2007 for use with Chem3D" and download the .zip file
ii) Extract mopac2007ultra.exe from the .zip file into: For v11: C:/Program Files/CambridgeSoft/ChemOffice2008/Common/COEA