Page add/remove component does not load

[FabianS.]

We have a virtual Server with the Parallels Infrastructure Manager. I activated the Plesk Panel. The software runs fine.
Then after about two weeks, running it as a mailserver i wanted to check out the horde webmailer.
I tried to go over: overview -> components add /remove.
When i clicked on the link, the browser resulted in a blank page.

Tried to find the error in the firewall and systemservices of the infrastructure manager because it redirects from:

https://myserver:8443/smb/update/add-components/
to
https://myserver:8447/add_components.html?secret=lbrahliyzvidsiogpsuh&locale=de-DE

But no result...

And i found no further information about this.

Thanks for any help