Laravel VerifyCsrfToken.php line 53 random on posts

I'm getting an 500 error from server randomly with some (not all!) post requests. After that error, I have to login.

I implemented PDF2HtmlEX that create html pages made with elements and resources like web fonts. To change page I make a post and get the data but after some page (not always the same) the ajax post return 500 and inside the data (and the log) I see the error:

[2015-12-21 22:17:48] local.ERROR: exception 'Illuminate\Session\TokenMismatchException' in /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/VerifyCsrfToken.php:53
Stack trace:
#0 [internal function]: Illuminate\Foundation\Http\Middleware\VerifyCsrfToken->handle(Object(Illuminate\Http\Request), Object(Closure))
#1 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#2 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/View/Middleware/ShareErrorsFromSession.php(49): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#3 [internal function]: Illuminate\View\Middleware\ShareErrorsFromSession->handle(Object(Illuminate\Http\Request), Object(Closure))
#4 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#5 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Session/Middleware/StartSession.php(62): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#6 [internal function]: Illuminate\Session\Middleware\StartSession->handle(Object(Illuminate\Http\Request), Object(Closure))
#7 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#8 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Cookie/Middleware/AddQueuedCookiesToResponse.php(37): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#9 [internal function]: Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse->handle(Object(Illuminate\Http\Request), Object(Closure))
#10 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#11 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Cookie/Middleware/EncryptCookies.php(59): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#12 [internal function]: Illuminate\Cookie\Middleware\EncryptCookies->handle(Object(Illuminate\Http\Request), Object(Closure))
#13 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#14 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/CheckForMaintenanceMode.php(44): Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#15 [internal function]: Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode->handle(Object(Illuminate\Http\Request), Object(Closure))
#16 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(124): call_user_func_array(Array, Array)
#17 [internal function]: Illuminate\Pipeline\Pipeline->Illuminate\Pipeline\{closure}(Object(Illuminate\Http\Request))
#18 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(103): call_user_func(Object(Closure), Object(Illuminate\Http\Request))
#19 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(122): Illuminate\Pipeline\Pipeline->then(Object(Closure))
#20 /path/to/laravel-project/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(87): Illuminate\Foundation\Http\Kernel->sendRequestThroughRouter(Object(Illuminate\Http\Request))
#21 /path/to/laravel-project/public/index.php(54): Illuminate\Foundation\Http\Kernel->handle(Object(Illuminate\Http\Request))
#22 {main}  

Like explaned in the documentation, I add...

<meta name="csrf-token" content="{{ csrf_token() }}">

in the app.blade.php master view templates. And at the start of js script I add:

  $.ajaxSetup({
    headers: {
      'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
    }
  });

I googled a lot and searched inside stackoverflow but I can't figure it out! The problem is that the error is occurring somethimes, not always: seems like there is a limit of checks that the token is considered valid.

I'm using laravel 5.1 (5.0 upgraded).

Have you any suggestions?

Thank you in advance!

via Chebli Mohamed