It seems that this error was caused by the wrong path for Genymotion, but actually it is caused by an error that prevents the Genymotion plugin from working with VirtualBox later than 4.2
To fix this error, all you have to do is go here: https://www.virtualbox.org/wiki/Download_Old_Builds_4_2 and download the version of VirtualBox version 4.2 for your OS. After reinstalling it, the error disappeared, and the Genymotion plugin correctly opened the list of devices
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