I had a specific error on the FNMS website in the past.
I just wanted to let you know how to possibly solve this issue.
The error was unspecific HTTP error 500.
I found out that after running the Powershell config script, the web.config under "C:\Program Files (x86)\Flexera Software\FlexNet Manager Platform\WebUI" has been changed and added some <customHeaders>.
The webserver IIS shows the specific error when going to "Sites->Suite->HTTP Response Headers"
The problem is that the Response Headers were inherited from the Default Website. So in the end there were duplicate Response Headers configured.
To solve this issue just check all Response Headers on the Default Website and comment out in the FNMS web.config.
After changing the web.config the error massage was obsolete.