I recently ran into a problem with a SharePoint Online site that had previously been created on BPOS and moved around through various iterations of Office 365. None of the site users had ever used the OneNote notebook associated with the site, but the link was present in the side navigation bar. When I tried to access it, I got the infamous “sorry, but something went wrong” error page. (For another day: discuss the Fisher-Price-ization of service error messages; the low information content doesn’t scare end users but makes it impossible to troubleshoot problems.)
A little binging turned up a plausible solution: “SharePoint 2013 OneNote Notebook something went wrong error“. I was a little leery of turning off the feature for fear that it wouldn’t turn back on. However, I took the plunge. After disabling the feature and re-enabling it, I was able to open the OneNote Online notebook, but I wasn’t able to use the “open in OneNote” link until I added some content in OneNote Online. All’s well that ends well. This may not be the only solution for this problem, but it has a 100% success rate for me so far.