I'm too embarrased. I was putting commas between the numbers in the margin: statements in the css file.
I've found a project intended to check epub compliance with standards (http://code.google.com/p/epub-conform/
). However, it is somewhat cumbersome to use (especially when you are trying to test iPad - adding hundreds of 'compliance' epubs is awkward.
Also, of the ones I've tried out with Calibre on the PC, most seem to indicate a non-conformance, but it's hard to see exactly what's happening.
I'm looking at using these as a basis for some longer epubs so that one can test compliance with only a few docs, but I'm not sure where I'm going to find the time