We have a datatype which wraps a user control. The YSOD below occurs on app start when the datatype is being inserted. When I hit the site again, the YSOD is gone, but the datatype is of the wrong type. I have to manually set it to the usercontrol again. 

Could not resolve a data type with id d15e1281-e456-4b24-aa86-1dda3e4299d5

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Could not resolve a data type with id d15e1281-e456-4b24-aa86-1dda3e4299d5

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[NullReferenceException: Could not resolve a data type with id d15e1281-e456-4b24-aa86-1dda3e4299d5]

   jumps.umbraco.usync.SyncDataType.Import(XmlNode xmlData, User u) +2325

   jumps.umbraco.usync.SyncDataType.ReadFromDisk(String path) +313

   jumps.umbraco.usync.uSync.RunSync() +276

   jumps.umbraco.usync.uSync.DoOnStart() +100

   Umbraco.Core.EnumerableExtensions.ForEach(IEnumerable`1 items, Action`1 action) +148

   Umbraco.Web.WebBootManager.Complete(Action`1 afterComplete) +124

[HttpException (0x80004005): Could not resolve a data type with id d15e1281-e456-4b24-aa86-1dda3e4299d5]

   System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app) +4057733

   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +191

   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +352

   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +407

   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +375

[HttpException (0x80004005): Could not resolve a data type with id d15e1281-e456-4b24-aa86-1dda3e4299d5]

   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +11702064

   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +141

   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4870277