Internal server error 500 with php files

[kess]

There's the error.
You can't have dual UserIDs and GroupIDs for the same domain.

Try to change vu2001 as follows:
vu2001:x:2001:2001:virtual-user:/var/www/virtual/old-nadherniludia.sk:/bin/false

and let me know if it works.

As I can understand, you only have 1 domain there, right ?