A little background: we are using the BCS with an external content type to expose external content we provide using a WCF service. We have a webpart that uses the external content type to display a list of data. Everything is working fine, but suddenly it stops. We cannot isolate the problem properly and are having a really hard time even reproducing it.
When the error occurs, we have checked our WCF service with a client application and there is no problem there, so we suspect it's actually the BCS that's giving us trouble.
We have to restart the BCS to get it working again. Sometimes it's enough to close the browser, causing me to think it might have to do with some session expering. I have googled to the end of the internet with the messages the ULS viewer is giving us, but to no avail.
Another relevent point might be that the user is logged in to the Sharepoint environment. It's aware of the users identity, but somehow can't make the trip to the BCS anymore. This can happen after two clicks, but also after using it for a couple of hours ;-(
I know this is very abstract, but it's what I have to work with. I can provide more details, but I am hoping this rings a bell to someone.
All suggestions are very very welcome, as I am fresh out of ideas.
EDIT I might be able to add the ULS trace later on, but I'm having difficulty to determine which messages are actually relevant.
The problem appears to popup everytime we do an IIS reset. Our WCF service is being deployed as part of the SharePoint web application. The BCS has trouble impersonation at times (I think), causing an access problem to the WCF service.
We moved the WCF service to an anonymous SharePoint web application and it looks like this resolved the issue (further testing needed). This obviously is a workaround, but may provide a hint as to what the actual problem is?