Error 500 - trace / error log

Hi,

Problem description :

- One External Server use POST Method to send datas to our internal Server (W2012 R2, IIS 8.5). 

- We have some errors (1 of 10 transactions approximately) on our internal Server.

Our .NET Agent view : 

- Method ReadEntityCoreSync timeout 35 secondes.

The IIS trace :

<EventData>
<Data Name="ContextId">{8003CA53-0007-F000-B63F-84710C7967BB}</Data>
<Data Name="BytesReceived">0</Data>
<Data Name="ErrorCode">2147943395</Data>
</EventData>

<EventData>
<Data Name="ContextId">{8003CA53-0007-F000-B63F-84710C7967BB}</Data>
<Data Name="BytesSent">0</Data>
<Data Name="ErrorCode">2147942487</Data>
</EventData>

-> Final Status : Error 500 

We have tested (without better result) :

- Disable Antivirus 

- SSL Settings (Client Ignore)

- No rule in Filtering 

Have you some ideas ?