I know many of us here love the Henle publications: the blue covers, creamy paper, and urtext editions.
I'm studying Beethoven's Piano Sonata #12, opus 26. I bought the single sonata from Henle, and I already had the complete volume that contains this sonata. I use the single sonata edition though, because it is thinner and easier to deal with. They have different editors and were produced decades apart. The single sonata edition is much newer - and that's the one where I found an error.
In the third movement, which is in Ab minor, there is a measure with an F flat in one hand and an F natural in the other. That didn't look, or sound, right. So I checked the complete volume and it had all F flats. I went to IMSLP and looked at some old editions and they all had F flats.
I went to the Henle website to see if there was an update or errata for this sonata, but nothing. On the contact page they had email addresses for some of the editors, and the editor for my Sonata was there. So I sent him an email, asking if there was an error.
I really didn't expect an answer, but less than 24 hours later, I got a response. He said that it was an error, that they knew about it already and were planning to correct it in the next print run.
I think that's a good result - they responded quickly and admitted the error. Not a completely positive result though, since it would be good to have a pdf file on the web page with a correction - that would have saved me some time and confusion.