Experiencing some intermittent failure notifications on a SharePoint workflow.  At first glance it appears to deal with an input format, but I'm having difficulty locating the culprit and I'm unable to replicate it.  If anyone has experienced an error like this or could help me decipher the message to help me locate the problem, I would gladly accept the help.  

RequestorId: e1e87a0a-36c3-e71e-0000-000000000000. Details: An unhandled exception occurred during the execution of the workflow instance. Exception details: System.FormatException: Input string was not in a correct format. at System.Number.ParseDouble(String value, NumberStyles options, NumberFormatInfo numfmt) at Microsoft.Activities.Expressions.ParseNumber`1.Execute(CodeActivityContext context) at System.Activities.CodeActivity`1.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation) Exception from activity ParseNumber<Double> IsEqualNumber<Double> If If Sequence NintexActivities.WorkflowXaml_a002d968_0889_4d8c_b705_00c13e50ffcd Sequence PickBranch Pick If Sequence While Wait for Task Sequence SingleTask_CreateListItemCancellationScope Sequence Microsoft.SharePoint.WorkflowServices.Activities.OperatingWebContextScope NintexActivities.WorkflowXaml_f6a19ad8_fae9_46e2_88bb_539a99b9e906 Evaluator Save as Draft Sequence If If If While State Machine Sequence Run If Sequence Flowchart Firefighter Evaluation Workflow Machine State Merge.WorkflowXaml_69f207dd_f3aa_4793_bd58_edff47c7b141