Problem with web.config and searches with special characters

Hi,

I have a problem with URL clean. When I do a search with, for example, "cuántico", Drupal return a unexpected error. However, if I disabled URL clean, I can make the search correctly.

URL not work: search/node/cuántico
URL work: ?q=search/node/cuántico

Only in the preproduction server give this error (IIS 7.5, customer requeriment), in local (Apache 2.2) work correctly.