PostgreSQL installation failure

Hello,

I need some help on an installation issue with PostgreSQL 9.5.0.1
I have written a wix bootstrapper to install postgresql for our
application.
This has worked for different version, but now we get sometimes trouble
with the installer as some sql scripts can't be executed during install.
From the logs I see an error 2 retunred from psql.exe

This error is found in the bitrock_installer.log from your original
installer
---
[14:58:49] Installing the adminpack module in the postgres database...
Executing C:\Program Files\PostgreSQL\9.5\bin\psql.exe -c "CREATE
EXTENSION adminpack" -d postgres
Script exit code: 2
---

and as well in our log where we try to launch some more sql scripts to
create a user, the database and the tables.
---
2016.08.02 14:59:07, Info , LaunchProcess(), Launch 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' with ' -U postgres --file "C:\Program
Files\PostgreSQL\9.5\Contest\CreateContestUser.sql"'.
2016.08.02 14:59:09, Info , LaunchProcess(), Standard output: ''
2016.08.02 14:59:09, Info , LaunchProcess(), Standard error: 'psql:
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (127.0.0.1) and
accepting
TCP/IP connections on port 5432?
'
2016.08.02 14:59:09, Info , LaunchProcess(), 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' returned: '2'.
2016.08.02 14:59:09, Error , InstallContestDB(), Contestdb not restored
-> create Contestdb and tables
2016.08.02 14:59:09, Info , LaunchProcess(), Launch 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' with ' -U postgres --file "C:\Program
Files\PostgreSQL\9.5\Contest\CreateContestDB.sql"'.
2016.08.02 14:59:11, Info , LaunchProcess(), Standard output: ''
2016.08.02 14:59:11, Info , LaunchProcess(), Standard error: 'psql:
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (127.0.0.1) and
accepting
TCP/IP connections on port 5432?
'
2016.08.02 14:59:11, Info , LaunchProcess(), 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' returned: '2'.
2016.08.02 14:59:11, Info , LaunchProcess(), Launch 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' with ' -U postgres --dbname Contestdb
--file "C:\Program
Files\PostgreSQL\9.5\Contest\CreateContestDBTables.sql"'.
2016.08.02 14:59:13, Info , LaunchProcess(), Standard output: ''
2016.08.02 14:59:13, Info , LaunchProcess(), Standard error: 'psql:
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (127.0.0.1) and
accepting
TCP/IP connections on port 5432?
'
2016.08.02 14:59:13, Info , LaunchProcess(), 'C:\Program
Files\PostgreSQL\9.5\bin\psql.exe' returned: '2'.
---

So far I wasn't able to reproduce this error by my self, but I know from
about 5 issues inside the last month.
As I'm not able to reproduce I would appreciate any help from you to find
out what causes this error.
All installations do run on Windows 7 Pro x64.

Best regards,
Thomas Deboben