500 19 183 31 errors

hello

the site works fine if I go directly to the page https://123.abc.com/apps/index1.php, but if try using https://123.abc.com i get 

500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed. or 500 19 183 31 errors in the logs.

Permission NTFS permissions look correct.

thanks