It looks like you are sending a malformed access token.
Your example, Vy*iWEzkfPKHAzx7PEtJcA%2529%2529 is not of the proper form and exhibits classic URI encoding corruption.
Valid tokens all seem to be 24 characters that end in )). And ) is often encoded as %29 by browsers depending on how you get it and/or cut and paste.
')' === decodeURIComponent ('%29')
Additionally, %25 is the URI encoding of %, so your token was double URI encoded. (That's two times too many. ;) )
When I send the same request, with a validly formatted token (which I have since deauthorized):
[/2.2/me?access_token=Vza4EEmVimmN4l3O9qZ87Q))...][1]
I get a valid result.
When I double URI-encode the token:
[/2.2/me?site=access_token=Vza4EEmVimmN4l3O9qZ87Q%2529%2529...][2]
I get the same 500 error that you got.
[1]: https://api.stackexchange.com/2.2/me?site=stackoverflow&access_token=Vza4EEmVimmN4l3O9qZ87Q))&key=U4DMV8nvpm3EOpvf69Rxw(( [2]: https://api.stackexchange.com/2.2/me?site=stackoverflow&access_token=Vza4EEmVimmN4l3O9qZ87Q%2529%2529&key=U4DMV8nvpm3EOpvf69Rxw((