Every once and a while you will receive a file that gives you ARX errors when you open it or try to run most common commands. These errors clog up the command line and are just a nuisance!  Here's the quick fix.

Open the affected file and escape out of any ARX errors that occur.  Enter WBLOCK at the command line, this command is not in the menus.  The Write Block dialogue box opens giving you several choices to make.  Start with selecting the Entire drawing radio button at the top Source section.  Next, pick the button to the right of the File name and path pulldown that has three dots.  Navigate to the same directory your drawing is in and give it a new file name, pick the save button, and finish the dialogue box out with a final selection of the OK button.  When the Confirm Export of Autodesk Map Data dialogue box appears select the No button.

You've just created a new file purged of all un-used entities, including the offending ARX entries!