A Plesk for Windows license assigned on MailEnable external service node can not be retrieved, we get the error:
Unable to retrieve the license key 'PLSK.*******.****!': The key with id=PLSK*********** failed to update: The version of your installed software is 11.5 for Unix/Linux, but the current license version is 10.0-* for Windows. Upgrades from 10.0-* for Windows to 11.5 for Unix/Linux are not available for this license.
The issue is caused by software issue ID PPA-2280 and was fixed in update #9 for Plesk Panel Automation 11.5: 11.5 MU#9.
Please update you PPA installation to latest version according to article.