We have a SharePoint 2010 installation where we installed a custom web service (using a .wsp) from a third party (so no access to the source). After installation everything worked fine. When we checked again after a couple of days, we got an error: "Request format is unrecognized for URL ending in " and then whatever operation we tried calling on the web service.
A quick web search suggested to add the HttpPost and HttpGet protocols through the web.config of this web service. We checked and they were already in place.
An application pool recycle fixed the problem. However the next day the problem was back and again an application pool recycle fixed the problem. Does anyone have any clue about how to troubleshoot this?