The preferences file may be corrupted / unwritable.
Run this application to fix your home directory privileges:
http://faqintosh.com/risorse/it/sys/rhp/If this does not work, follow these steps to reset:
Restart your computer.
Open the terminal and type the following lines:
rm ~/Library/Preferences/com.mixage.qmidi2.plist
rm ~/Library/Preferences/com.mixage.qmidipro.plist
Launch QMidi
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www.mixagesoftware.com
support@mixagesoftware.com