Okey, somewhat progress.
I found out that when i disable my main domain, the only domain with a purchased ssl certificate then alle the webstats on the other domains work again.
Anyone who knows why?
UPDATE
Found some logs that are related.
nginx error.log:
2013/08/07 18:44:31 [error] 28668#0: *4418 SSL_do_handshake() failed (SSL: error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol) while SSL handshaking to upstream, client: 95.96.116.87, server: ***.**, request: "GET /plesk-stat/webstat/ HTTP/1.1", upstream: "https://**IP**:7081/plesk-stat/webstat/", host: "***.**"
2013/08/07 18:44:31 [error] 28668#0: *4419 SSL_do_handshake() failed (SSL: error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol) while SSL handshaking to upstream, client: 95.96.116.87, server: ***.**, request: "GET /favicon.ico HTTP/1.1", upstream: "https://**IP**:7081/favicon.ico", host: "***.**"
this might be related too
httpd error_log
[Mon Aug 05 22:04:41 2013] [warn] RSA server certificate CommonName (CN) `***.**' does NOT match server name!?
[Mon Aug 05 22:04:41 2013] [warn] Init: (***.**:443) You configured HTTP(80) on the standard HTTPS(443) port!
[Mon Aug 05 22:04:41 2013] [warn] Init: (***.**:443) You configured HTTP(80) on the standard HTTPS(443) port!
[Mon Aug 05 22:04:41 2013] [warn] Init: Name-based SSL virtual hosts only work for clients with TLS server name indication support (RFC 4366)