Modernbill 4.x & Windows Plesk API problem: Access is denied. (Error code 5) at Unable to connect to pipe

If you face this error: Access is denied. (Error code 5) at Unable to connect to pipe \\.\pipe\psapipe , the solution is very easy

First give full perms at  C:\Windows\system32\cmd.exe  to user psaadm and
at C:\Inetpub\vhosts\the domain you have the api\cgi-bin\ to user IWPD_1(your_name)

then

Go to IIS administration console, right click on the application pool
that your wrapper resides in, and click properties.

Click on the identify tab and select ‘Predefined – Local System’
This will fix your permission issues but it might be best to create
a seperate application pool for the wrapper for security reasons.