No web service found at ... Random exception issue

Question

Hi,

in production env I randomly, several times per day, recieve following error:

Exception type:InvalidOperationException
Exception details:
Source: System.Web.Extensions
Message: No web service found at: path/servicename.asmx.

I log it in Application_Error method. It happens when url request is :

https://path/servicename.asmx/js 

Googling didn't help :/ Any ideas what could be causing that issue?

Thanks, Pawel