Thanks for the quick answer!!
Hm, what do you mean exactly? The path is already in the windows environmental variable "Path". I guess calibre adds this path automatically during the installation process, right?
Or do you mean something else? Is there any PHP-setting? I checked the whole php.ini, but didn't find anything that would help.
By the way - talking about php.ini: Safe mode is off! (hm, maybe I should change that some other time
As I wrote: It wouldn't be so strange, if the old CalibreForLRF wouldn't work either (along with some other EXE-programs I am using with PHP on the same server).