Spontaneous Server Errors During AngularJS $http calls - angularjs

Question

I'm building an SPA in AngularJS served by a Laravel (5.1) backend. Of late I've been encountering an annoying error, a server 500 or code 0 error which is abit hard to explain how it comes but let me try to may be someone will understand the dental formula of my problem.
When i start my AngularJS controller, I make several server calls (via independent $http calls from services) to retrieve information i might later need in the controller. For example,
Functions.getGrades()
.then(function(response)
{
$scope.grades = response.data;
});
Subjects.offered()
.then(function(response)
{
$scope.subjects = response.data;
});
Later on i pass these variables (grades or subjects) to a service where they are used for processing. However, these functions are randomly returning code 500 server errors after they run, and sometimes returning status code 0 after running. This happens in a random way and it is hard for me to point out the circumstances leading to their popping up. This leaves me with frequent empty Laravel-ised error screens like the ones shown below.
Anyone reading my mind?

Answer 1

Ok, after a suggestion given in a comment above that I check my Laravel log files (located in storage/logs/laravel.log- Laravel 5.1), i found out that the main error most of these times was this one: 'PDOException' with message 'SQLSTATE[HY000] [1044] Access denied for user ''#'localhost' to database 'forge'' in ..., plus another one that paraphrased something like No valid encrypter found. These were the key opener.
On reading another SO thread here, it said in part:
I solved, sometimes laravel not read APP_KEY in .ENV. And returns a value "SomeRandomString" (default is defined in config / app.php), and have the error "key length is invalid", so the solution is to copy the value of APP_KEY, to the value 'key 'in config / app.php, that's all! I solved!
That was exactly the issue! When loading the DB params from the .env to config/database.php, Laravel was sometimes unable to read the environment variables and went for the fallback default fallback options (forge for DB name and username and SomeRandomString for the APP_KEY). So, to solve this i just did as advised: copied the APP_KEY in .env to the config/app.php and edited the default DB parameters to the actual DB name and username/password I'm using. Just that and i was free from pollution. Hope someone finds this helpful.