Error 503 Service Unavailable when upload file

Would anyone can help me with this error, I make an ajax request to complete the upload.

The application is accessed by customers outside of our network, when the error sometimes the solution is to make a f5 several times in the pages and try again. When access by vs2013 works well and within the network as well.

I am using the window server 2008 and IIS 7.

I am using the angular js to the request

app pool config

general

1. .net framework version : v4.0
2. managed pipeline : integrated
3. name: portal
4. queue: length : 1000
5. start automaticaly: true

cpu

1. limit : 0
2. limit action: noaction
3. limit interval (minutes) : 5
4. processor affinity enabled : false
5. processor affinity mask : 4294967295

process model

1. identity : networkservice
2. idle time-out (minutes) : 20
3. load user profile true
4. maximum worker process : 1
5. ping enabled : true
6. pig maximum reponse time (seconds) : 90
7. ping period (seconds) : 30
8. shutdown time limit (seconds) : 90
9. startut time limit (seconds) : 90

process orphaning

1. enabled : false
2. executable : 
3. executable parameters :

rapid fail protection

1. service unavalable response type : httplevel
2. enabled : true
3. failure interval (minutes) : 5
4. maximum failures :  5
5. shutdown executable :
6. shutdown executable parameters : 

recycling

1. disabled overlappedrecycle : false
2. disabled recycling for configuration changes : false
3. General recycle event long entty
   1. application pool configuration changed : false
   2. isapi reported unhealthy : false
   3. manual recycle : false
   4. private memory limit exceeded : true
   5. regular time interval : true
   6. request limit exceeded : false
   7. specific time : false
   8. virtual memory limit exceeded : true
4. private memory limit (kb) : 0
5. regular time interval (minutes) : 1740
6. request limit : 0
7. specific times : timestamp
8. virtual memory limit (kb) : 0