I have edited an existing form to remove a couple of unwanted fields. But now when I try to submit the same form I get this error:

[InvalidOperationException:
The property __field_5639 exists on both the old and new definitions but does not have the same type and is not convertible between the types.]
at EPiServer.Data.Dynamic.StoreDefinition.RemapChanges(IDictionary`2 copyTypeBag, IList`1 newMappings, List`1 dataMoves)
at EPiServer.Data.Dynamic.StoreDefinition.Remap(IDictionary`2 typeBag, StoreDefinitionParameters parameters)
at EPiServer.Forms.Core.Data.DdsPermanentStorage.RemapStore(FormIdentity formIden, IDictionary`2 typesBag, StoreDefinitionParameters storeParams)
at EPiServer.Forms.Core.Data.DdsPermanentStorage.SaveToStorage(FormIdentity formIden, Submission submission)
at EPiServer.Forms.Core.Internal.DataSubmissionService.StoreSubmissionData(String sFormSubmissionId, FormIdentity formIden, Submission submission)
at EPiServer.Forms.Core.Internal.DataSubmissionService.PerformDataSubmit(NameValueCollection rawSubmittedData, HttpContextBase httpContext, ControllerBase controller)
at EPiServer.Forms.Controllers.DataSubmitController.Submit()
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass15.b__12()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
at System.Web.Mvc.Controller.ExecuteCore()
at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
at EPiServer.Forms.Controllers.FormsMvcHandler.ProcessController(IController controller)
at EPiServer.Forms.Controllers.FormsMvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

I can't see any reference to __field_5639 in the markup of the page/form, so I don't know where it is coming from. I am assuming that it is somewhere in the database.

Is there a way I can reset this form?