I have two dashboards with custom drilldown search. One of them works just fine. But the other returns a blank page; looking into the SID I can see this error:
error:133 - Masking the original 404 message: 'Unexpected query string parameters: earliest, q, latest' with 'Page not found!' for security reasons
This actually happens to most custom drilldown searches that I try to set up, no matter which dashboard.
I use a CNAME for my server. If I change the URL to use the canonical name of the server, the "security" error goes away. Although this kind of makes sense, it doesn't explain why some custom searches do not trigger this problem. In the problematic dashboard, it fails even the simplest search like sourcetype = this, i.e., no special character of any type.