Regarding error in levelsetsegmentation

[Naga Teja Athava]

Hi, 

  I am using vmtk in ubuntu  to segement the blood vessel using this link http://www.vmtk.org/tutorials/ImageBasedModeling.html ,but while i was trying to input lower threshold value , the gui is refreshing rapidly and not taking input command

Automatic piping vmtklevelsetsegmentation
Parsing options vmtklevelsetsegmentation
    ImageInputFileName = image_volume_voi.vti
    LevelSetsOutputFileName = level_sets.vti
Explicit piping vmtklevelsetsegmentation
Input vmtklevelsetsegmentation members:
    Id = 0
    Disabled = 0
    Image = None
    ImageInputFileName = image_volume_voi.vti
    FeatureImage = None
    FeatureImageInputFileName =
    InitializationImage = None
    InitializationImageInputFileName =
    InitialLevelSets = None
    InitialLevelSetsInputFileName =
    LevelSets = None
    LevelSetsInputFileName =
    LevelSetsType = geodesic
    FeatureImageType = gradient
    NegateForInitialization = 0
    SigmoidRemapping = 0
    IsoSurfaceValue = 0.0
    DerivativeSigma = 0.0
    FeatureDerivativeSigma = 0.0
    UpwindFactor = 1.0
    FWHMRadius = [1.0, 1.0, 1.0]
    FWHMBackgroundValue = 0.0
    NumberOfIterations = 0
    PropagationScaling = 0.0
    CurvatureScaling = 0.0
    AdvectionScaling = 1.0
    EdgeWeight = 0.0
    SmoothingIterations = 5
    SmoothingTimeStep = 0.1
    SmoothingConductance = 0.8
    vmtkRenderer = None
    LevelSetsOutputFileName = level_sets.vti
    FeatureImageOutputFileName =
Reading VTK XML image file.
Spacing 0.433594 0.433594 0.650000
Origin 101.000000 240.699997 1644.589966
Dimensions 256 299 156
Executing vmtklevelsetsegmentation ...
Please choose initialization type:
0: colliding fronts;
1: multiple colliding fronts;
2: fast marching;
3: threshold;
4: isosurface;
5: seed;
Colliding fronts initialization.
Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): Please input lower threshold ('n' for none): 

Can anyone help resolving this issue

Thank you

Athava Naga Teja