Can you show the error that is visible before that?

Thanks for the answer. The very first error is:

Error: [$compile:ctreq] http://errors.angularjs.org/1.2.28/$compile/ctreq?p0=ngSwitch&p1=ngSwitchDefault at Error (native) at https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:121:450 at t (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:166:369) at J (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:169:409) at g (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:162:256) at https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:161:377 at link (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:313:58) at J (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:169:373) at g (https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:162:256) at https://example.org/piwik/index.php?module=Proxy&action=getCoreJs&cb=17d88d1f7e8b5fb30c1beb23d87c739e:161:377 <!-- ngSwitchDefault: -->

Thx! Hard to tell how this can happen. Can you maybe have a look at the system check? Can you maybe also have a look at the "Network" tab to see if there's a request that fails?

Maybe also have a look here: http://piwik.org/faq/troubleshooting/faq_18485/ Are you using pagespeed or so?

Ah, I see. Same as #5081 - pagespeed was enabled. After disabling it, it works again. Thanks.