Unable to open profile manager; postgres error

After several days of trying today I was able to connect a network user to the server, but now I'm not able to open the profile manager. It shows the error message:

Caught exception "Connection to DB failed" [CSDatabaseError] executing route /auth/?redirect=https://mac.ars.private/devicemanagement/api/authentication/callback:
(
0 CoreFoundation 0x00007fff9790f25c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff928d8e75 objc_exception_throw + 43
2 CSService 0x0000000105df59bd -[CSConnectionPool openConnection] + 3309
3 CSService 0x0000000105df638a -[CSConnectionPool currentConnection] + 98
4 CSService 0x0000000105e85329 -[CSAuthService unauthenticatedSession] + 82
5 CSService 0x0000000105e85903 -[CSAuthService currentOrNewSession] + 154
6 CSService 0x0000000105e75c71 +[CSHTTPRouteHelper setCurrentSessionForRequest:] + 264
7 CSService 0x0000000105e7fc09 __21-[CSAuthService init]_block_invoke + 367
8 CSService 0x0000000105e7181a __53-[CSRoutingHTTPConnection httpResponseForMethod:URI:]_block_invoke + 95
9 CSService 0x0000000105e74d6c -[CSHTTPBackgroundResponse bounce:] + 286
10 Foundation 0x00007fff8df2d76b __NSThread__main__ + 1318
11 libsystem_pthread.dylib 0x00007fff8dce7899 _pthread_body + 138
12 libsystem_pthread.dylib 0x00007fff8dce772a _pthread_struct_init + 0
13 libsystem_pthread.dylib 0x00007fff8dcebfc9 thread_start + 13
)

The server is freshly installed and after setting up DNS, OD and a group and user, I'd liked to setup the profiles for the users. After opening the profile manager all I see is the error message above. All I've done after activating the Profile Manager was "Standard Configuration: Including Configuration for Services" and "Sign Configuration Profile".

All i found in the community is that I have to back up all data, delete Server.app and restore it from the backup. Than launch and reinstate services. But the thread ist from december 2012 and I'm hoping, that there's another way to make it work.

Thanks in advance for all hints, tipps and tricks to make it work as it should.