Any URL Rewrite causes application error

Hello everyone! Weird problem here.

After installing the URL Rewrite module (IIS 7), I've found that having ANY URL Rewrite rules (even when they are disabled) causes an webservice application to fail with "The page cannot be displayed because an internal server error has occurred."

Here's what happens:

Visit myurl.com/webservice.asmx
Works fine.

'Sites' -> 'Default Web Site' -> 'URL Rewrite' -> Add Rule

Name: test
Matches, exact match
Pattern: test
Action: redirect
Redirect URL: test2

Apply.

Visit myurl.com/webservice.asmx
'The page cannot be displayed because an internal server error has occurred.'

Visit myurl.com/test
Redirects to myurl.com/test2, causes 404 (expected)

Disable the rule.

Visit myurl.com/webservice.asmx
'The page cannot be displayed because an internal server error has occurred.'

Remove the rule, leaving no remaining rules in the URL rewrite listing.

Visit myurl.com/webservice.asmx
Works fine.

Any ideas? Thanks!