The Secret of Access Denied

A client contacted us and said that he could not install EurekaLog. More precisely: EurekaLog is installed, but subsequent launch of the IDE raises an error:

Can't load package C:\Program Files (x86)\Neos Eureka S.r.l\EurekaLog 7\Packages\Studio25\EurekaLogExpert250.bpl. Access is denied.

Moreover, the client claimed that the file exists, there is access to it, reinstalling EurekaLog does not help.