thanks for the reply nigel - its difficult to get advice a lot of the time when using an old synth! However, I swear by the ESQ1 and have used it for over 10 years now. I think after a while old synths become like instruments - every one has its own unique sound, especially when you start pushing it to its limits.

Now your advice sounds reassuring - that my data may be fine.

I'll just keep the SYSEX file stored until I find a solution - no point wasting weeks of fruitless research. Apparently SX has "issues" with Sysex and this will be fixed (apparently) shortly.

My main concern is that the data is safe.

Now for some more questions...

What set-up are you using?
Is there any program to slow the transmission speed? I read that Cakewalk may be able to do it - but I haven't tested it yet. What kind of value should I be looking for for the transmission speed?
If the data was corrupted, could I tell? I mean do I tell what corruptd data looks like?

... so many questions. But your help is greatly appreciated!