System.FormatException: Input string was not in a correct format.
  at System.Number.StringToNumber (System.String str, System.Globalization.NumberStyles options, System.Number+NumberBuffer& number, System.Globalization.NumberFormatInfo info, System.Boolean parseDecimal) [0x00057] in <c8d0d7b9135640958bff528a1e374758>:0
  at System.Number.ParseInt32 (System.String s, System.Globalization.NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00013] in <c8d0d7b9135640958bff528a1e374758>:0
  at System.Int32.Parse (System.String s) [0x00007] in <c8d0d7b9135640958bff528a1e374758>:0
  at BetterContracts.BetterContractsBehaviour.<PrioritiseAllContracts>m__0 (WorkItem c) [0x00026] in <5e48dd863f334ee2bb95e0df64d6cd2d>:0
  at System.Linq.EnumerableSorter`2[TElement,TKey].ComputeKeys (TElement[] elements, System.Int32 count) [0x00010] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at System.Linq.EnumerableSorter`1[TElement].ComputeMap (TElement[] elements, System.Int32 count) [0x00000] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at System.Linq.EnumerableSorter`1[TElement].Sort (TElement[] elements, System.Int32 count) [0x00000] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at System.Linq.OrderedEnumerable`1[TElement].SortedMap (System.Linq.Buffer`1[TElement] buffer) [0x00006] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at System.Linq.OrderedEnumerable`1[TElement].ToList () [0x0001f] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at System.Linq.Enumerable.ToList[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x0001f] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at BetterContracts.BetterContractsBehaviour.PrioritiseAllContracts (System.Collections.Generic.List`1[T] contracts) [0x000e2] in <5e48dd863f334ee2bb95e0df64d6cd2d>:0