The Yamaha AN1x Synthesizer mailing list

Jim's got a great point about dust being an enemy... but I'd also like to 
suggest considering the sensitivity of the MIDI input section of the 
AN1x.  My setup has a MIDI patchbay which is very useful but often 
confuses the AN1x.  When confused, it displays "Illegal Data".  We've 
called the MIDI police but they don't know what charge to place on the 
offending synth.  :-)

There's been a lot of discussion on this list concerning the sysex 
response and various MIDI cards.  I had a similar problem where the synth 
would lock up during patch bank dumps to it.  A different MIDI card 
(actually a joystick port converter) solved the lockups.

The assumption of the group is generally that the AN1x can't handle 
certain data rates or dropped packets or something of that sort.  So you 
might try using a MIDI data stream analyzer program (MIDIOX is a good 
one) to see if there are any irregularities.