I have just got rid of the problem.
i've got MS-Excel 64 bit.
I had turned ON the advanced option:
(File/Options -> Advanced -> General ->)
Ignore other applications that use Dynamic Data Exchange (DDE)
I did that to get rid of the
cannot use object linking and embedding
error when starting Excel.
I consequently found that the problem with this error was that something had changed the DCOM User to my account instead of the launching User
(Component services\Computers\Mycomputer\DComConfig\Microsoft Excel Application-> Properties (right click) -> Identity (tab) change
this user to the launching user)
When I did that cannot use object linking and embedding was gone, but
There was a Problem sending the command to the program
was shown up each time I tried to double click an Excel file.
Finally I turned
Ignore other applications that use Dynamic Data Exchange (DDE)
back ON
and now everything seems to be fine!
Hope that helps