jimDicken I'm wondering if there is a receive event size limit in ST4 causing this issue (SYSEX Learn)? With ST3 it was only ever receiving smaller MIDI events but now with SYSEX, there is the possibility of MUCH larger chunks of data.
 
Voice select is nice and small - F0 43 73 01 52 25 11 00 02 00 02 F7 - which probably explains why that one works
Song select is not so small - F0 43 73 01 52 26 03 00 00 00 55 73 65 72 3A 2F 48 41 52 4D 4F 4E 59 20 47 55 59 53 20 53 4F 55 4E 44 53 2F 41 72 6D 73 20 4F 66 20 4D 61 72 79 5F 47 2D 41 5F 48 47 2E 54 31 37 34 2E 72 67 74 00 F7
I suspect (touch wood) that will be an easy fix when Peter gets back from holidays.