PHP + AJAX cannot upload files larger than 100KB

Uploading files larger than around 100KB fails with 500 server error. The site is built on Laravel and is using AJAX for file uploading. Small files can be loaded without problems.

I have tested uploading with the same image that is scaled with GIMP to smaller than 100KB and another one which is scaled bigger than 100KB, so the problem cannot be file type or anything related to image itself instead the problem seems to be related only to file size.

I have checked php.ini for max memory, upload_max_filesize, post_max_size and all are fine. I have also checked that apache virtualhost is not having max file size configuration. I have checked apache logs and it shows only 500 server error without anymore details. I cannot find any clue in any other log file. I have debugged the jQuery to AJAX call and ensured that the called function on PHP side is not being called. I have tried to check Laravel configurations, but couldn't find anything that could be related.

Any ideas where the file size limit could be coming from? Or any ideas where to get more information where the 500 is coming from?

UPDATE: here are the request details for successful and failing request. The image is same just scaled under 100KB in successful case and over 100KB in failing case.

Successful request:

Request URL:http://example.com/upload_photo
Request Method:POST
Status Code:200 OK
Request Headersview source
Accept:application/json, text/javascript, */*; q=0.01
Accept-Encoding:gzip,deflate
Accept-Language:en-US,en;q=0.8,fi;q=0.6
Connection:keep-alive
Content-Length:119826
Content-Type:multipart/form-data; boundary=----WebKitFormBoundaryhVIN89yYhJPjWZoS
Cookie:step1=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; step2=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; step3=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; laravel_session=b6cc316fdb17ada3552da4168fa23ad35bc0f171%2B4nKoS74bQHSD9HjzIytxL3Tno2sBYbOKRPfemvHY
Host:example.com
Origin:http://example.com
Referer:http://example.com/album/21095
User-Agent:Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36
X-Requested-With:XMLHttpRequest
Request Payload
------WebKitFormBoundaryhVIN89yYhJPjWZoS
Content-Disposition: form-data; name="0"; filename="1c.jpg"
Content-Type: image/jpeg


------WebKitFormBoundaryhVIN89yYhJPjWZoS--
Response Headersview source
Connection:Keep-Alive
Content-Encoding:gzip
Content-Length:42
Content-Type:text/html
Date:Wed, 24 Sep 2014 01:20:09 GMT
Keep-Alive:timeout=5, max=99
Server:Apache/2.2.22 (Ubuntu)
Vary:Accept-Encoding
X-Powered-By:PHP/5.3.10-1ubuntu3.10

Failing request:

Request URL:h_t_t_p://example.com/upload_photo
Request Method:POST
Status Code:500 Internal Server Error
Request Headersview source
Accept:application/json, text/javascript, */*; q=0.01
Accept-Encoding:gzip,deflate
Accept-Language:en-US,en;q=0.8,fi;q=0.6
Connection:keep-alive
Content-Length:142451
Content-Type:multipart/form-data; boundary=----WebKitFormBoundarycv7BVPR9y5npZxAB
Cookie:step1=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; step2=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; step3=d18d6d9cb707914642cc3df4501565c5c361feab%2B1; laravel_session=b6cc316fdb17ada3552da4168fa23ad35bc0f171%2B4nKoS74bQHSD9HjzIytxL3Tno2sBYbOKRPfemvHY
Host:example.com
Origin:http://example.com
Referer:http://example.com/album/21095
User-Agent:Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36
X-Requested-With:XMLHttpRequest
Request Payload
------WebKitFormBoundarycv7BVPR9y5npZxAB
Content-Disposition: form-data; name="0"; filename="1d.jpg"
Content-Type: image/jpeg


------WebKitFormBoundarycv7BVPR9y5npZxAB--
Response Headersview source
Accept-Ranges:bytes
Connection:close
Content-Encoding:gzip
Content-Length:829
Content-Type:text/html
Date:Wed, 24 Sep 2014 01:21:42 GMT
ETag:"141df4-73b-5030bebf5947d"
Last-Modified:Sun, 14 Sep 2014 19:57:01 GMT
Server:Apache/2.2.22 (Ubuntu)
Vary:Accept-Encoding