It suddenly happened that whenever I tried to open an Excel file(.xlsx), I always received the following error message:
“There was a problem sending the command to the program”
Excel just opened itself without opening the actual xlsx file, which was very annoying.
I finally came to the solution: Open the Microsoft Office program and open its Options window.in Advanced tab un-check “Ignore other applications that use Dynamic Data Exchange (DDE)” option and restart Excel.
Below is the link I followed(solution 1 fixed my problem)