Today we got solved an error which looked a bit weird in YapWatcher log:
Microsoft.TeamFoundation.WorkItemTracking.Client.FileAttachmentException: Attachment upload failed. Check that you have a network connection and that the Team Foundation Server is available. If the problem persists, contact your Team Foundation Server administrator. ---> System.Net.WebException: The server committed a protocol violation. Section=ResponseHeader Detail=CR must be followed by LF at System.Net.HttpWebRequest.GetResponse() at Microsoft.TeamFoundation.WorkItemTracking.Proxy.ClientService.UploadFileInternal(FileAttachment fileAttachment, Boolean allowWriteStreamBuffering) at Microsoft.TeamFoundation.WorkItemTracking.Proxy.ClientService.UploadFile(FileAttachment fileAttachment)
at Microsoft.TeamFoundation.WorkItemTracking.Client.AttachmentCollection.Save(String areaNodeUri, String projectUri)
Have not seen this one before, but this turned out to be an database issue: SQL Server behind TFS was running out of disk space.
This came from TFS 2008 Server.