A properly work external list start displaying error message Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator.
Correlation ID:a59ea712-175c-4430-a588-de32b6b0806c
Checking SharePoint logs indicate there is a change in a data type of one of column
SharePoint Log
11/05/2013 09:17:49.27 w3wp.exe (0x12F8) 0x0E94 SharePoint Foundation Web Parts 89a1 High Error while executing web part: Microsoft.BusinessData.MetadataModel.InvalidMetadataObjectException: The Serialization failed because the actual object type (which is ‘System.String’) is not the same as the type indicated (which is ‘System.Byte[]’) in the type descriptor with id ‘767’ and name ‘image’. at Microsoft.SharePoint.BusinessData.Runtime.FieldValueHelpers.SerializeElement(ITypeDescriptor td, ITypeReflector tr, Object dataSource, XmlWriter xw, Boolean ignoreInsignificants, String
To fix this being on the exeternal list design page click on the table you have the list and remove all the operations then recreate them back again.
Then the external list start displaying properly.
