With a bit of trial & error, I've found a fix for it.
It needs a bit of tweaking in the registry.
I'll make this as simple as possible, for anyone not up to speed on editing the registry.
Click, 'Start' then 'Run' and type regedit in the box. click 'ok'
The first entry is HKEY_CLASSES_ROOT, navigate down till you find 'Applications', and from there down to 'imix.exe'
You'll see an entry called 'shell'. Highlight it and then click on the (Default) entry, right click and pick Modify.
You'll see a blank box. Type the word Play
Highlight shell again, right click, and pick New, & Key
Call the new key Play
Highlight Play, right click, and pick New, & Key
Call the new key Command
Look under Open\Command at the (default) value, it will say;
"D:\Program Files\Acoustica MP3 Audio Mixer\iMix.exe" "%1" (Your drive might not be D:)
Leave that entry as it is, and using copy & paste, copy it from there to the (default) value under Play\Command
but...... once it's pasted in....
REMOVE THE TWO QUOTE MARKS SURROUNDING %1 AT THE END OF THE LINE
now just close the registry by clicking the X in the top right corner.
Works for me. Hope it works for you.
By the way, whatever you do, DO NOT remove the quote marks from the original entry under Open\Command. That will just screw things up.