Update:
The problem persist in version 2.3.
I'm on Windows 7. I found a workarround to get the interface installed.
I run the FTPbox with windows XP SP3 compatibility mode enabled. Then in the options pannel I check to install the web interface and it work properly. After that I can disable the compatibility mode.
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This is most likely a permissions-problem. Try running the app as administrator instead, it should work.
I'll make sure to fix this in the near future!
Update:
The problem persist in version 2.3.
I'm on Windows 7. I found a workarround to get the interface installed.
I run the FTPbox with windows XP SP3 compatibility mode enabled. Then in the options pannel I check to install the web interface and it work properly. After that I can disable the compatibility mode.