VB: The given key was not present in the dictionary

good evening,

I've encountered a confusing error, which I am unable to fight on my own. I'd appreciate your help.

I have two inputs of DataTree:
y is composed of 2-level DataTree, 3 branches and under each one you find a bunch of different items (curves).
x contains more complicated structure (DataTree), only by one level though. So I got again 3 branches, each has a couple of sub-branches and then on each sub-branch there are two items (points).

What I wanted to do is to find a closest point from both points on each sub-branch to every curve on the same branch.

 Private Sub RunScript(ByVal x As DataTree(Of Point3d), ByVal y As DataTree(Of Curve), ByVal prm As Object, ByVal ttl As Object, ByRef A As Object)
    Dim j,i,e As New Integer

    For i = 0 To y.BranchCount - 1
      For e = 0 To x.BranchCount - 1

        Dim pth As New GH_Path(i, e)
        Dim pth1 As New GH_Path(i, e)
        Dim pt As Point3d = x.Item(pth, 0)
        Dim pt1 As Point3d = x.Item(pth, 1)

        For j = 0 To y.Branch(i).Count - 1
          Dim t,t1,dist As New Double
          y.Branch(i).item(j).ClosestPoint(pt, t)
          y.Branch(i).item(j).ClosestPoint(pt1, t1)
          dist = pt.distanceTo(y.Branch(i).item(j).PointAt(t))
          dist += pt.distanceTo(y.Branch(i).item(j).PointAt(t1))
'code would continue here with a "if-statement"
        Next
      Next
    Next

  End Sub

When I run this, I get an error: The given key was not present in the dictionary.
It all started with an addition of x.Item(pth,0). I struggled addressing the actual items at the end of my DataTree. I usually handle only two levels, so I get by with Branch(i).item(j)..

Any ideas? It's probably something trivial.