[otrs] Error when creating a ticket or article

Hi all. After updating to 2.4.7 I get set of strange errors when trying to create a new ticket or article. First of all I get the prompt "Open index.pl" (You want to download the following file...) as if the mime type .pl wasn't defined. The delivered file is empty though, which explains why the file type isn't recognized.

From time to time (can't find the regularity here, though I guess there is one), there's the following error message instead:

Can't use string ("10") as an ARRAY ref while "strict refs" in use at /opt/otrs//Kernel/System/Ticket/Event/TimeUpdate.pm line 88. Oddly enough the ticket/article is properly created. Any hints? Greets, Daniel