Ah, OK - thanks Ray. I got it working with the jquery / Bloom validation, rather than the server validations.
I'm away now so can't double check, but I'm sure it was working on my desktop, but wasn't on my laptop. But the code in the PM below was missing. I added that and it worked again, with the Bloom styling and positioning. (It had been working without it I'm sure, just with the default position and style of the validation message.)
Not sure why, but don't suppose it matters now that it seems OK.