In SharePoint 2010 Service Pack 1, we are having trouble with ListData.svc. In most cases, it correctly returns data from a list. However, there are a few lists which don't work and instead return the following error (friendly error messages turned off):
<?xml version="1.0" encoding="utf-8" standalone="yes" ?> - <error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"> <code /> <message xml:lang="en-US">An error occurred while processing this request.</message> </error>
Where can I start with troubleshooting? I cannot see any place where anything useful is logged.
Edit 17/03/2016: I've noticed that the lists are quite large: they range from having between 33,000 and 116,000 items. Could this potentially be the issue?
Edit 18/03/2016: I've been advised that the farm administrator was creating new content types and running the Content Type Hub Publisher/Subscriber jobs manually before the issue occurred. Could this be a clue?
Edit 21/03/2016: I've noticed that all lists have a "Last Modified" time of "2 weeks ago", which roughly lines up with the time that the new content types were created (see edit above on 18/3/2016)
Edit 21/03/2016 @ 3pm: OK, bear with me here... I saved a copy of the problem list to a new template. I then instantiated a new list using the template, and the listdata.svc displayed the list correctly (though it was empty). HOWEVER, as soon as I add a single new item to this list it fails to display in listdata.svc. When I delete this item, the list starts working again through listdata.svc (even though it's empty). I even tried removing almost all fields so that it would be similar to a very basic list type, and it still had problems. What could this indicate?
Edit 23/03/2016: For some reason, the listdata.svc will start returning values if the "Title" column is not empty. However, this is new behaviour, since in my particular list the Title field has allowed empty values for a long time previously. What could have changed?
Edit 4/4/2015: I've turned on Failed Request Tracing, and get the following back (not sure how helpful this is). Kind of getting desperate here... :
HttpReason: Internal Server Error
ErrorCode: The operation completed successfully. (0x0)
Edit 27/4/2016: There was no resolution: the business decided to create PowerShell scripts to automatically set Title values to a single space character (" ") for all items every day, before listdata.svc could be used by an external application