We have been making quite a bit of use of InfoPath forms recently and have published successfully to a number of sites across our farm.  However yesterday I tried to publish to a new site and got this error:

The following URL is not valid: https://…….

After a lot of googling I confirmed that this was not an uncommon error, but none of the scenarios matched our situation; i.e. we already have a root site and have been publishing successfully for some time, and could still publish to other sites.

After trying some test the culprit seems to be the Office SharePoint Server Publishing Infrastructure feature!

• trying to publish to sites which have Office SharePoint Server Publishing Infrastructure enabled throws this error
• publishing to a subsite which does not have Office SharePoint Server Publishing Infrastructure enabled works fine

It would have been nice to have seen this documented somewhere when I googled, but I suppose that is the danger of just searching.