In the Access 2010 Beta, if you open a file from an Explorer window or a shortcut, you get the dreaded
The command or action '' isn't available now.
But the app works perfectly after dismissing that message. This one had me stumped; tried decompile, compile & save, compact & repair; nothing fixed it. Luckily a few minutes of Googling revealed the answer: if you open that same file from within Access you don't get that message.
So then, to prevent that message all you have to do is create a shortcut that launches Access and opens the file, like this (watch for line breaks):
"C:\Program Files\Microsoft Office\Office14\MSACCESS.EXE" C:\mydatabase.mdb