I already followed the advice here, but even when this setting is ticked I can't open any of my Excel files any longer:
Even after I ticked that box and restarted my computer. Now I get this message each time I try to open an Excel file:
There was a problem sending the command to the program.
The message I got from the beginning is this:
Microsoft Excel is waiting for another application to complete an OLE action.
It started after I had saved the Excel as html and then uploaded to my website several times.