Is there a fibre bundle with fibre homeomorphic to $\mathbb R^k$ which cannot be given the structure of a vector bundle?
Solution 1:
This question is answered here :https://mathoverflow.net/questions/104869/examples-for-open-disc-bundle-which-is-not-vector-bundle
Quoting the mathoverflow question:
William Browder showed in "Open and closed disc bundles", Ann. of Math. (2) 83 (1966), 218-230 that there are open disc bundles over some complex which cannot be isomorphic to a vector bundle.
Theorem 1 of the above paper gives the desired counterexample.