The scatter_ docs name the arguments as:
Tensor.scatter_(dim, index, src, reduce=None) → Tensor

so the second argument is expected to be a LongTensor as also mentioned in the docs:
        dim (int) – the axis along which to index

        index (LongTensor) – the indices of elements to scatter, can be either empty or of the same dimensionality as src. When empty, the operation returns self unchanged.

        src (Tensor or float) – the source element(s) to scatter.

        reduce (str, optional) – reduction operation to apply, can be either 'add' or 'multiply'.

Based on the stack trace it seems that your custom Dataset uses the scatter_ operation in the __getitem__:
  File "E:\pyprojects\MICCAI19-MedVQA-master\dataset_RAD.py", line 243, in __getitem__
    target.scatter_(0, labels, scores)

so you would need to change labels to a LongTensor via:
    target.scatter_(0, labels.long(), scores)