CRM 2013: Select EntityImage via OData gives Generic SQL error

Hi,

I am trying to retrieve a contacts EntityImage property via OData. Therefore I use an URL similar to/XrmServices/2011/OrganizationData.svc/ContactSet(GUID'%7B1B4E0141-C8CE-E311-A66F-842B2B6792E8%7D')?$select=EntityImage

While this works fine for users with system administrator role, there is an error for "standard" users. If I have a look at the network trace, there is an HTTP 500 response coming up, the XML Response is:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata">
  <code>-2147204784</code>
  <message xml:lang="de-DE">Generic SQL error.</message>
</error>

Am I missing special privileges here? Unfortunately I am not able to trace on SQL Server side, since I do not have access to the customers SQL Server.