Error: 502 Duplicate data

Hi,
Ive had an issue where we get an Error 502 when trying to save a lead with a duplicate name.

The Espo Log says :
[2016-11-04 14:41:07] Espo.ERROR: API [POST]:/:controller, Params:Array ( [controller] => Lead ) .......
[2016-11-04 14:41:07] Espo.ERROR: Display Error: {"reason":"Duplicate","data": .......

PHP Log:
"POST /api/v1/index.php" 409 796

Apache Log:
"POST /api/v1/Lead HTTP/1.0" 409 4736

**I can send the whole log privately if you need it .

I don't know why this is happening. Can you help me.

Thank you